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• Determine if a decimal can be stored as int32

  - by anchandra

  I am doing some custom serializing, and in order to save some space, i want to serialize the decimals as int, if possible value wise. Performance is a concern, since i am dealing with a high volume of data. The current method i use is: if ((value > Int32.MinValue) && (value < Int32.MaxValue) && ((valueAsInt = Decimal.ToInt32(value)) == value)) { return true; } Can this be improved?

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• Decimal rounding strategies in enterprise applications

  - by Sapphire

  Well, I am wondering about a thing with rounding decimals, and storing them in DB. Problem is like this: Let's say we have a customer and a invoice. The invoice has total price of $100.495 (due to some discount percentage which is not integer number), but it is shown as $100.50 (when rounded, just for print on invoice). It is stored in the DB with the price of $100.495, which means that when customer makes a deposit of $100.50 it will have $0.005 extra on the account. If this is rounded, it will appear as $0, but after couple of invoices it would keep accumulating, which would appear wrong (although it actually is not). What is best to do in this case. Store the value of $100.50, or leave everything as-is?

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• Validate decimal number in (known) national format

  - by Álvaro G. Vicario

  PHP has many built-in functions to validate numbers but they all expect input in computer format: 1234.56. I need to validate stuff like 1,234.56 (English) or 1.234,56 (Spanish), together with some typical attributes (accepted range, max number of decimals, etc.). I started writing my own function but I soon got lost. It's easy to read the user input into a float variable but I want to be able to detect numbers with invalid formats like 1,23456.7 or 1..25. Do you have any recommendation on the subject? (Decimal and thousand characters are known beforehand and it's okay to hard-code digit groups as three, there's no need to cover Indian number format.)

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• how to exit recursive math formula and still get an answer

  - by calccrypto

  i wrote this python code, which from wolfram alpha says that its supposed to return the factorial of any positive value (i probably messed up somewhere), integer or not: from math import * def double_factorial(n): if int(n) == n: n = int(n) if [0,1].__contains__(n): return 1 a = (n&1) + 2 b = 1 while a<=n: b*=a a+= 2 return float(b) else: return factorials(n/2) * 2**(n/2) *(pi/2)**(.25 *(-1+cos(n * pi))) def factorials(n): return pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(2*n) the problem is , say i input pi to 6 decimal places. 2*n will not become a float with 0 as its decimals any time soon, so the equation turns out to be pi**(.5 * sin(n*pi)**2) * 2**(-n + .25 * (-1 + cos(2*n*pi))) * double_factorial(loop(loop(loop(...))))) how would i stop the recursion and still get the answer? ive had suggestions to add an index to the definitions or something, but the problem is, if the code stops when it reaches an index, there is still no answer to put back into the previous "nests" or whatever you call them

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• How to change active culture on Windows Phone 7

  - by Sam

  [Update] I see I need the full example to explain. In my Windows Phone 7 App, I got a page containing a TextBox bound to a Decimal "Amount": <TextBox Text="{Binding Amount,Mode=TwoWay}" InputScope="CurrencyAmount"/> The phone settings are set to German. In german localization, a value like 1234.56m would be formatted 1.234,56 (unlike the US, where it should be 1,234.56). Problem is, when I enter a value like 1.234,56 in the textbox, the content will be interpreted for US, resulting in 1.23456m, when it should have been 1234.56m. So, how do I get the binding on the WP7 to use the current phone culture instead of a generic US one? In Germany people expect to enter a colon for decimals instead of a dot.

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• How one decision can turn web services to hell

  - by DigiMortal

  In this posting I will show you how one stupid decision may turn developers life to hell. There is a project where bunch of complex applications exchange data frequently and it is very hard to change something without additional expenses. Well, one analyst thought that string is silver bullet of web services. Read what happened. Bad bad mistake In the early stages of integration project there was analyst who also established architecture and technical design for web services. There was one very bad mistake this analyst made: All data must be converted to strings before exchange! Yes, that’s correct, this was the requirement. All integers, decimals and dates are coming in and going out as strings. There was also explanation for this requirement: This way we can avoid data type conversion errors! Well, this guy works somewhere else already and I hope he works in some burger restaurant – far away from computers. Consequences If you first look at this requirement it may seem like little annoying piece of crap you can easily survive. But let’s see the real consequences one stupid decision can cause: hell load of data conversions are done by receiving applications and SSIS packages, SSIS packages are not error prone and they depend heavily on strings they get from different services, there are more than one format per type that is used in different services, for larger amounts of data all these conversion tasks slow down the work of integration packages, practically all developers have been in hurry with some SSIS import tasks and some fields that are not used in different calculations in SSAS cube are imported without data conversions (by example, some prices are strings in format “1.021 $”). The most painful problem for developers is the part of data conversions because they don’t expect that there is such a stupid requirement stated and therefore they are not able to estimate the time their tasks take on these web services. Also developers must be prepared for cases when suddenly some service sends data that is not in acceptable format and they must solve the problems ASAP. This puts unexpected load on developers and they are not very happy with it because they can’t understand why they have to live with this horror if it is possible to fix. What to do if you see something like this? Well, explain the problem to customer and demand special tasks to project schedule to get this mess solved before going on with new developments. It is cheaper to solve the problems now that later.

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• How far should an entity take care of its properties values by itself?

  - by Kharlos Dominguez

  Let's consider the following example of a class, which is an entity that I'm using through Entity Framework. - InvoiceHeader - BilledAmount (property, decimal) - PaidAmount (property, decimal) - Balance (property, decimal) I'm trying to find the best approach to keep Balance updated, based on the values of the two other properties (BilledAmount and PaidAmount). I'm torn between two practices here: Updating the balance amount every time BilledAmount and PaidAmount are updated (through their setters) Having a UpdateBalance() method that the callers would run on the object when appropriate. I am aware that I can just calculate the Balance in its getter. However, it isn't really possible because this is an entity field that needs to be saved back to the database, where it has an actual column, and where the calculated amount should be persisted to. My other worry about the automatically updating approach is that the calculated values might be a little bit different from what was originally saved to the database, due to rounding values (an older version of the software, was using floats, but now decimals). So, loading, let's say 2000 entities from the database could change their status and make the ORM believe that they have changed and be persisted back to the database the next time the SaveChanges() method is called on the context. It would trigger a mass of updates that I am not really interested in, or could cause problems, if the calculation methods changed (the entities fetched would lose their old values to be replaced by freshly recalculated ones, simply by being loaded). Then, let's take the example even further. Each invoice has some related invoice details, which also have BilledAmount, PaidAmount and Balance (I'm simplifying my actual business case for the sake of the example, so let's assume the customer can pay each item of the invoice separately rather than as a whole). If we consider the entity should take care of itself, any change of the child details should cause the Invoice totals to change as well. In a fully automated approach, a simple implementation would be looping through each detail of the invoice to recalculate the header totals, every time one the property changes. It probably would be fine for just a record, but if a lot of entities were fetched at once, it could create a significant overhead, as it would perform this process every time a new invoice detail record is fetched. Possibly worse, if the details are not already loaded, it could cause the ORM to lazy-load them, just to recalculate the balances. So far, I went with the Update() method-way, mainly for the reasons I explained above, but I wonder if it was right. I'm noticing I have to keep calling these methods quite often and at different places in my code and it is potential source of bugs. It also has a detrimental effect on data-binding because when the properties of the detail or header changes, the other properties are left out of date and the method has no way to be called. What is the recommended approach in this case?

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• Working the Chart Percentages

  - by Tim Dexter

  Charting in BIP is such fun, well sometimes it is. Not so much today, at least not for Ron in San Diego. He needed a horizontal bar chart showing values plotted for various test areas with value labels at the end of the bars. Simple enough right? The wrinkle, they were percentage values so he needed to see '56%' not '56'! Still, it should be simple enough but the percentage formatting has a requirement for your values to be in a decimal format i.e. 0.56 not 56.0. 56.0 gets formatted as 5600%. OK, so either pull the values out as decimals or use the div function to divide the values in the chart by 100 e.g. <xsl:value-of select="myval div 100)" /> Now I can use the following the chart XML to format the percentages as I need them:   <Graph ... > ... <MarkerText visible="true"> <Y1ViewFormat> <ViewFormat numberType="NUMTYPE_PERCENT" decimalDigit="0" numberTypeUsed="true" leadingZeroUsed="true" decimalDigitUsed="true"/> </Y1ViewFormat> </MarkerText> ... </Graph>   That gets me the values shown the way I want but the auto axis formatting gets me from 0 >> 1. I now need to go in and add the formatting for the axis too.   <Graph ...> ... <Y1Axis axisMinAutoScaled="false" axisMinValue="0.0" axisMaxAutoScaled="false" axisMaxValue="1.0" majorTickStepAutomatic="true"> <ViewFormat numberType="NUMTYPE_PERCENT" decimalDigit="0" scaleFactor="SCALEFACTOR_NONE" numberTypeUsed="true" leadingZeroUsed="true" decimalDigitUsed="true" scaleFactorUsed="true"/> </Y1Axis>   Now I have a chart that's showing the percentage values and formatting axis scale correctly for me too. You can of course mess with the attributes above to get more decimal points on your labels, etc. Happy Charting!

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• Backing up my Windows Home Server to the Cloud&hellip;

  - by eddraper

  Ok, here’s my scenario: Windows Home Server with a little over 3TB of storage.  This includes many years of our home network’s PC backups, music, videos, etcetera. I’d like to get a backup off-site, and the existing APIs and apps such as CloudBerry Labs WHS Backup service are making it easy.  Now, all it’s down to is vendor and the cost of the actual storage.   So,  I thought I’d take a lazy Saturday morning and do some research on this and get the ball rolling.  What I discovered stunned me…   First off, the pricing for just about everything was loaded with complexity.  I learned that it wasn’t just about storage… it was about network usage, requests, sites, replication, and on and on. I really don’t see this as rocket science.  I have a disk image.  I want to put it in the cloud.  I’m not going to be be using it but once daily for incremental backups.  Sounds like a common scenario.  Yes, if “things get real” and my server goes down, I will need to bring down a lot of data and utilize a fair amount of vendor infrastructure.  However, this may never happen.  Offsite storage is an insurance policy.   The complexity of the cost structures, perhaps by design, create an environment where it’s incredibly hard to model bottom line costs and compare vendor all-up pricing.  As it is a “lazy Saturday morning,” I’m not in the mood for such antics and I decide to shirk the endeavor entirely.  Thus, I decided to simply fire up calc.exe and do some a simple arithmetic model based on price per GB.  I shuddered at the results.  Certainly something was wrong… did I misplace a decimal point?  Then I discovered CloudBerry’s own calculator.   Nope, I hadn’t misplaced those decimals after all.  Check it out (pricing based on 3174 GB):   Amazon S3 $398.00 per month $4761 per year Azure $396.75 per month $4761 per year Google $380.88 per month $4570.56 per year   Conclusion: Rampant crack smoking at vendors.  Seriously.  Out. Of. Their. Minds. Now, to Amazon’s credit, vision, and outright common sense, they had one offering which directly addresses my scenario:   Amazon Glacier $31.74 per month $380.88 per year   hmmm… It’s on the table.  Let’s see what it would cost to just buy some drives, an enclosure and cart them over to a friend’s house.   2 x 2TB Drives from NewEgg.com $199.99   Enclosure $39.99     $239.98   Carting data to back and forth to friend’s within walking distance pain   Leave drive unplugged at friend’s $0 for electricity   Possible data loss No way I can come and go every day.     I think I’ll think on this a bit more…

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• Green (Screen) Computing

  - by onefloridacoder

  I recently was given an assignment to create a UX where a user could use the up and down arrow keys, as well as the tab and enter keys to move through a Silverlight datagrid that is going be used as part of a high throughput data entry UI. And to be honest, I’ve not trapped key codes since I coded JavaScript a few years ago.  Although the frameworks I’m using made it easy, it wasn’t without some trial and error.    The other thing that bothered me was that the customer tossed this into the use case as they were delivering the use case.  Fine.  I’ll take a whack at anything and beat up myself and beg (I’m not beyond begging for help) the community for help to get something done if I have to. It wasn’t as bad as I thought and I thought I would hopefully save someone a few keystrokes if you wanted to build a green screen for your customer.   Here’s the ValueConverter to handle changing the strings to decimals and then back again.  The value is a nullable valuetype so there are few extra steps to take.  Usually the “ConvertBack()” method doesn’t get addressed but in this case we have two-way binding and the converter needs to ensure that if the user doesn’t enter a value it will remain null when the value is reapplied to the model object’s setter.  1: using System; 2: using System.Windows.Data; 3: using System.Globalization; 4:  5: public class NullableDecimalToStringConverter : IValueConverter 6: { 7: public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 8: { 9: if (!(((decimal?)value).HasValue)) 10: { 11: return (decimal?)null; 12: } 13: if (!(value is decimal)) 14: { 15: throw new ArgumentException("The value must be of type decimal"); 16: } 17:  18: NumberFormatInfo nfi = culture.NumberFormat; 19: nfi.NumberDecimalDigits = 4; 20:  21: return ((decimal)value).ToString("N", nfi); 22: } 23:  24: public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture) 25: { 26: decimal nullableDecimal; 27: decimal.TryParse(value.ToString(), out nullableDecimal); 28:  29: return nullableDecimal == 0 ? null : nullableDecimal.ToString(); 30: } 31: }            The ConvertBack() method uses TryParse to create a value from the incoming string so if the parse fails, we get a null value back, which is what we would expect.  But while I was testing I realized that if the user types something like “2..4” instead of “2.4”, TryParse will fail and still return a null.  The user is getting “puuu-lenty” of eye-candy to ensure they know how many values are affected in this particular view. Here’s the XAML code.   This is the simple part, we just have a DataGrid with one column here that’s bound to the the appropriate ViewModel property with the Converter referenced as well. 1: <data:DataGridTextColumn 2: Header="On-Hand" 3: Binding="{Binding Quantity, 4: Mode=TwoWay, 5: Converter={StaticResource DecimalToStringConverter}}" 6: IsReadOnly="False" /> Nothing too magical here.  Just some XAML to hook things up.   Here’s the code behind that’s handling the DataGridKeyup event.  These are wired to a local/private method but could be converted to something the ViewModel could use, but I just need to get this working for now. 1: // Wire up happens in the constructor 2: this.PicDataGrid.KeyUp += (s, e) => this.HandleKeyUp(e);   1: // DataGrid.BeginEdit fires when DataGrid.KeyUp fires. 2: private void HandleKeyUp(KeyEventArgs args) 3: { 4: if (args.Key == Key.Down || 5: args.Key == Key.Up || 6: args.Key == Key.Tab || 7: args.Key == Key.Enter ) 8: { 9: this.PicDataGrid.BeginEdit(); 10: } 11: }   And that’s it.  The ValueConverter was the biggest problem starting out because I was using an existing converter that didn’t take nullable value types into account.   Once the converter was passing back the appropriate value (null, “#.####”) the grid cell(s) and the model objects started working as I needed them to. HTH.

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• SharePoint: Numeric/Integer Site Column (Field) Types

  - by CharlesLee

  What field type should you use when creating number based site columns as part of a SharePoint feature? Windows SharePoint Services 3.0 provides you with an extensible and flexible method of developing and deploying Site Columns and Content Types (both of which are required for most SharePoint projects requiring list or library based data storage) via the feature framework (more on this in my next full article.) However there is an interesting behaviour when working with a column or field which is required to hold a number, which I thought I would blog about today. When creating Site Columns in the browser you get a nice rich UI in order to choose the properties of this field: However when you are recreating this as a feature defined in CAML (Collaborative Application Mark-up Language), which is a type of XML (more on this in my article) then you do not get such a rich experience.  You would need to add something like this to the element manifest defined in your feature: <Field SourceID="http://schemas.microsoft.com/sharepoint/3.0"        ID="{C272E927-3748-48db-8FC0-6C7B72A6D220}"        Group="My Site Columns"        Name="MyNumber"        DisplayName="My Number"        Type="Numeric"        Commas="FALSE"        Decimals="0"        Required="FALSE"        ReadOnly="FALSE"        Sealed="FALSE"        Hidden="FALSE" /> OK, its not as nice as the browser UI but I can deal with this. Hang on. Commas="FALSE" and yet for my number 1234 I get 1,234.  That is not what I wanted or expected.  What gives? The answer lies in the difference between a type of "Numeric" which is an implementation of the SPFieldNumber class and "Integer" which does not correspond to a given SPField class but rather represents a positive or negative integer.  The numeric type does not respect the settings of Commas or NegativeFormat (which defines how to display negative numbers.)  So we can set the Type to Integer and we are good to go.  Yes? Sadly no! You will notice at this point that if you deploy your site column into SharePoint something has gone wrong.  Your site column is not listed in the Site Column Gallery.  The deployment must have failed then?  But no, a quick look at the site columns via the API reveals that the column is there.  What new evil is this?  Unfortunately the base type for integer fields has this lovely attribute set on it: UserCreatable = FALSE So WSS 3.0 accordingly hides your field in the gallery as you cannot create fields of this type. However! You can use them in content types just like any other field (except not in the browser UI), and if you add them to the content type as part of your feature then they will show up in the UI as a field on that content type.  Most of the time you are not going to be too concerned that your site columns are not listed in the gallery as you will know that they are there and that they are still useable. So not as bad as you thought after all.  Just a little quirky.  But that is SharePoint for you.

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• Investigating on xVelocity (VertiPaq) column size

  - by Marco Russo (SQLBI)

    In January I published an article about how to optimize high cardinality columns in VertiPaq. In the meantime, VertiPaq has been rebranded to xVelocity: the official name is now “xVelocity in-memory analytics engine (VertiPaq)” but using xVelocity and VertiPaq when we talk about Analysis Services has the same meaning. In this post I’ll show how to investigate on columns size of an existing Tabular database so that you can find the most important columns to be optimized. A first approach can be looking in the DataDir of Analysis Services and look for the folder containing the database. Then, look for the biggest files in all subfolders and you will find the name of a file that contains the name of the most expensive column. However, this heuristic process is not very optimized. A better approach is using a DMV that provides the exact information. For example, by using the following query (open SSMS, open an MDX query on the database you are interested to and execute it) you will see all database objects sorted by used size in a descending way. SELECT * FROM $SYSTEM.DISCOVER_STORAGE_TABLE_COLUMN_SEGMENTS ORDER BY used_size DESC You can look at the first rows in order to understand what are the most expensive columns in your tabular model. The interesting data provided are: TABLE_ID: it is the name of the object – it can be also a dictionary or an index COLUMN_ID: it is the column name the object belongs to – you can also see ID_TO_POS and POS_TO_ID in case they refer to internal indexes RECORDS_COUNT: it is the number of rows in the column USED_SIZE: it is the used memory for the object By looking at the ration between USED_SIZE and RECORDS_COUNT you can understand what you can do in order to optimize your tabular model. Your options are: Remove the column. Yes, if it contains data you will never use in a query, simply remove the column from the tabular model Change granularity. If you are tracking time and you included milliseconds but seconds would be enough, round the data source column to the nearest second. If you have a floating point number but two decimals are good enough (i.e. the temperature), round the number to the nearest decimal is relevant to you. Split the column. Create two or more columns that have to be combined together in order to produce the original value. This technique is described in VertiPaq optimization article. Sort the table by that column. When you read the data source, you might consider sorting data by this column, so that the compression will be more efficient. However, this technique works better on columns that don’t have too many distinct values and you will probably move the problem to another column. Sorting data starting from the lower density columns (those with a few number of distinct values) and going to higher density columns (those with high cardinality) is the technique that provides the best compression ratio. After the optimization you should be able to reduce the used size and improve the count/size ration you measured before. If you are interested in a longer discussion about internal storage in VertiPaq and you want understand why this approach can save you space (and time), you can attend my 24 Hours of PASS session “VertiPaq Under the Hood” on March 21 at 08:00 GMT.

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• Investigating on xVelocity (VertiPaq) column size

  - by Marco Russo (SQLBI)

    In January I published an article about how to optimize high cardinality columns in VertiPaq. In the meantime, VertiPaq has been rebranded to xVelocity: the official name is now “xVelocity in-memory analytics engine (VertiPaq)” but using xVelocity and VertiPaq when we talk about Analysis Services has the same meaning. In this post I’ll show how to investigate on columns size of an existing Tabular database so that you can find the most important columns to be optimized. A first approach can be looking in the DataDir of Analysis Services and look for the folder containing the database. Then, look for the biggest files in all subfolders and you will find the name of a file that contains the name of the most expensive column. However, this heuristic process is not very optimized. A better approach is using a DMV that provides the exact information. For example, by using the following query (open SSMS, open an MDX query on the database you are interested to and execute it) you will see all database objects sorted by used size in a descending way. SELECT * FROM $SYSTEM.DISCOVER_STORAGE_TABLE_COLUMN_SEGMENTS ORDER BY used_size DESC You can look at the first rows in order to understand what are the most expensive columns in your tabular model. The interesting data provided are: TABLE_ID: it is the name of the object – it can be also a dictionary or an index COLUMN_ID: it is the column name the object belongs to – you can also see ID_TO_POS and POS_TO_ID in case they refer to internal indexes RECORDS_COUNT: it is the number of rows in the column USED_SIZE: it is the used memory for the object By looking at the ration between USED_SIZE and RECORDS_COUNT you can understand what you can do in order to optimize your tabular model. Your options are: Remove the column. Yes, if it contains data you will never use in a query, simply remove the column from the tabular model Change granularity. If you are tracking time and you included milliseconds but seconds would be enough, round the data source column to the nearest second. If you have a floating point number but two decimals are good enough (i.e. the temperature), round the number to the nearest decimal is relevant to you. Split the column. Create two or more columns that have to be combined together in order to produce the original value. This technique is described in VertiPaq optimization article. Sort the table by that column. When you read the data source, you might consider sorting data by this column, so that the compression will be more efficient. However, this technique works better on columns that don’t have too many distinct values and you will probably move the problem to another column. Sorting data starting from the lower density columns (those with a few number of distinct values) and going to higher density columns (those with high cardinality) is the technique that provides the best compression ratio. After the optimization you should be able to reduce the used size and improve the count/size ration you measured before. If you are interested in a longer discussion about internal storage in VertiPaq and you want understand why this approach can save you space (and time), you can attend my 24 Hours of PASS session “VertiPaq Under the Hood” on March 21 at 08:00 GMT.

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• Good grammar for date data type for recursive descent parser LL(1)

  - by Totophil

  I'm building a custom expression parser and evaluator for production enviroment to provide a limited DSL to the users. The parser itself as the DSL, need to be simple. The parser is going to be built in an exotic language that doesn't support dynamic expression parsing nor has any parser generator tools available. My decision is to go for recursive descent approach with LL(1) grammar, so that even programmers with no previous experience in evaluating expression could quickly learn how the code works. It has to handle mixed expressions made up of several data types: decimals, percentages, strings and dates. And dates in the format of dd/mm/yyyy are easy to confuse with a string of devision ops. Is where a good solution to this problem? My own solution that is aimed at keeping the parser simple involves prefixing dates with a special symbol, let's say apostrophe: <date> ::= <apostr><digit><digit>/<digit><digit>/<digit><digit><digit><digit> <apostr> ::= ' <digit> ::= '0'..'9'

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• iPhone SDK - UITabBarConroller and custom design

  - by Cheryl

  Hi I am having a problem with my tab bars at the bottom of the screen. The designer has decided it should be one colour (not black) when inactive and another colour when active. I have worked out how to replace the main colour of the tabbar by subclassing UITabBarController and doing this:- - (void)viewDidLoad { [super viewDidLoad]; CGRect frame = CGRectMake(0.0, 0, self.view.bounds.size.width, self.view.bounds.size.height); UIView *v = [[UIView alloc] initWithFrame:frame]; //get percentage values from digitalcolour meter and enter as decimals v.backgroundColor = [UIColor colorWithRed:.0 green:.706 blue:.863 alpha:1]; [tabBar1 insertSubview:v atIndex:0]; [v release]; } I just can't see how to make the active tabbar be a separate colour when it is selected. I have tried subclassing UITabBarItem but there doesn't seem to be any property for me to set to change the background colour of the tab. They also want to have the icons on the tab bar not be blue and grey and I can't figure out how to do that. In the ViewController for one tab bar item I have put this into viewdidload:- myTabBarItem *tabItem = [[myTabBarItem alloc] initWithTitle:@"listOOO" image:[UIImage imageNamed:@"starcopy.png"] tag:1]; tabItem.customHighlightedImage=[UIImage imageNamed:@"starcopy.png"]; self.tabBarItem=tabItem; [tabItem release]; tabItem=nil; and in my subclass of UITabBarItem I have put this:- -(UIImage *) selectedImage{ return self.customHighlightedImage; } Only I don't see the icon at all. If I put this into the viewDidLoad of my subclass of UITabBarController:- for (UITabBarItem *item in tabBar1.items){ item.image = [UIImage imageNamed:@"starcopy.png"]; } Then all my tab bars have the icon but they are blue (and grey when inactive) how would I get them not to become blue but stay their original colour? If you have any light on this problem please help as I have been banking my head on the wall for 2 days now and it's getting me down. Thanks in advance Cheryl

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• Compression algorithm for IEEE-754 data

  - by David Taylor

  Anyone have a recommendation on a good compression algorithm that works well with double precision floating point values? We have found that the binary representation of floating point values results in very poor compression rates with common compression programs (e.g. Zip, RAR, 7-Zip etc). The data we need to compress is a one dimensional array of 8-byte values sorted in monotonically increasing order. The values represent temperatures in Kelvin with a span typically under of 100 degrees. The number of values ranges from a few hundred to at most 64K. Clarifications All values in the array are distinct, though repetition does exist at the byte level due to the way floating point values are represented. A lossless algorithm is desired since this is scientific data. Conversion to a fixed point representation with sufficient precision (~5 decimals) might be acceptable provided there is a significant improvement in storage efficiency. Update Found an interesting article on this subject. Not sure how applicable the approach is to my requirements. http://users.ices.utexas.edu/~burtscher/papers/dcc06.pdf

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• Required Working Precision for the BBP Algorithm?

  - by brainfsck

  Hello, I'm looking to compute the nth digit of Pi in a low-memory environment. As I don't have decimals available to me, this integer-only BBP algorithm in Python has been a great starting point. I only need to calculate one digit of Pi at a time. How can I determine the lowest I can set D, the "number of digits of working precision"? D=4 gives me many correct digits, but a few digits will be off by one. For example, computing digit 393 with precision of 4 gives me 0xafda, from which I extract the digit 0xa. However, the correct digit is 0xb. No matter how high I set D, it seems that testing a sufficient number of digits finds an one where the formula returns an incorrect value. I've tried upping the precision when the digit is "close" to another, e.g. 0x3fff or 0x1000, but cannot find any good definition of "close"; for instance, calculating at digit 9798 gives me 0xcde6 , which is not very close to 0xd000, but the correct digit is 0xd. Can anyone help me figure out how much working precision is needed to calculate a given digit using this algorithm? Thank you,

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• Poor DB4O performance - What am I doing wrong?

  - by Jon

  I read Rob Conery's post about Object databases and thought I'd give it a go. I have a class lets say Book with 15 properties mostly string, some int, one Datetime and 2 decimals. I used Rob's code to open the database file etc to test on a Winforms project not a Web project. So I did the following: for(int i = 0; i < 1000000; i++) { var Book = new Book(); //Assign variables s.Save(Book); } s.CommitChanges(); This took at least a couple of minutes. I then tried to retrieve all data to test speed: var spp = s.All<Passports>(); This one line was quick, however, then doing: sppp.Count() as well as a seperate test doing a foreach loop and incrementing a counter took a couple of minutes. This seems quite slow to me. Am I doing something wrong or am I expecting too much?

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• Fastest way to modify a decimal-keyed table in MySQL?

  - by javanix

  I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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• smallest mysql type that accomodates single decimal

  - by donpal

  Database newbie here. I'm setting up a mysql table. One of the fields will accept a value in increment of a 0.5. e.g. 0.5, 1.0, 1.5, 2.0, .... 200.5, etc. I've tried int but it doesn't capture the decimals. `value` int(10), What would be the smallest type that can accommodate this value, considering it's only a single decimal. I also was considering that because the decimal will always be 0.5 if at all, I could store it in a separate boolean field? So I would have 2 fields instead. Is this a stupid or somewhat over complicated idea? I don't know if it really saves me any memory, and it might get slower now that I'm accessing 2 fields instead of 1 `value` int(10), `half` bool, //or something similar to boolean What are your suggestions guys? Is the first option better, and what's the smallest data type in that case that would get me the 0.5?

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• Fastest way to convert a list of doubles to a unique list of integers?

  - by javanix

  I am dealing with a MySQL table here that is keyed in a somewhat unfortunate way. Instead of using an auto increment table as a key, it uses a column of decimals to preserve order (presumably so its not too difficult to insert new rows while preserving a primary key and order). Before I go through and redo this table to something more sane, I need to figure out how to rekey it without breaking everything. What I would like to do is something that takes a list of doubles (the current keys) and outputs a list of integers (which can be cast down to doubles for rekeying). For example, input {1.00, 2.00, 2.50, 2.60, 3.00} would give output {1, 2, 3, 4, 5). Since this is a database, I also need to be able to update the rows nicely: UPDATE table SET `key`='3.00' WHERE `key`='2.50'; Can anyone think of a speedy algorithm to do this? My current thought is to read all of the doubles into a vector, take the size of the vector, and output a new vector with values from 1 => doubleVector.size. This seems pretty slow, since you wouldn't want to read every value into the vector if, for instance, only the last n/100 elements needed to be modified. I think there is probably something I can do in place, since only values after the first non-integer double need to be modified, but I can't for the life of me figure anything out that would let me update in place as well. For instance, setting 2.60 to 3.00 the first time you see 2.50 in the original key list would result in an error, since the key value 3.00 is already used for the table.

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• TSQL - make a literal float value

  - by David B

  I understand the host of issues in comparing floats, and lament their use in this case - but I'm not the table author and have only a small hurdle to climb... Someone has decided to use floats as you'd expect GUIDs to be used. I need to retrieve all the records with a specific float value. sp_help MyTable -- Column_name Type Computed Length Prec -- RandomGrouping float no 8 53 Here's my naive attempt: --yields no results SELECT RandomGrouping FROM MyTable WHERE RandomGrouping = 0.867153569942739 And here's an approximately working attempt: --yields 2 records SELECT RandomGrouping FROM MyTable WHERE RandomGrouping BETWEEN 0.867153569942739 - 0.00000001 AND 0.867153569942739 + 0.00000001 -- 0.867153569942739 -- 0.867153569942739 In my naive attempt, is that literal a floating point literal? Or is it really a decimal literal that gets converted later? If my literal is not a floating point literal, what is the syntax for making a floating point literal? EDIT: Another possibility has occurred to me... it may be that a more precise number than is displayed is stored in this column. It may be impossible to create a literal that represents this number. I will accept answers that demonstrate that this is the case. EDIT: response to DVK. TSQL is MSSQLServer's dialect of SQL. This script works, and so equality can be performed deterministically between float types: DECLARE @X float SELECT top 1 @X = RandomGrouping FROM MyTable WHERE RandomGrouping BETWEEN 0.839110948199148 - 0.000000000001 AND 0.839110948199148 + 0.000000000001 --yields two records SELECT * FROM MyTable WHERE RandomGrouping = @X I said "approximately" because that method tests for a range. With that method I could get values that are not equal to my intended value. The linked article doesn't apply because I'm not (intentionally) trying to straddle the world boundaries between decimal and float. I'm trying to work with only floats. This isn't about the non-convertibility of decimals to floats.

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• Scala and Java BigDecimal

  - by geejay

  I want to switch from Java to a scripting language for the Math based modules in my app. This is due to the readability, and functional limitations of mathy Java. For e.g, in Java I have this: BigDecimal x = new BigDecimal("1.1"); BigDecimal y = new BigDecimal("1.1"); BigDecimal z = x.multiply(y.exp(new BigDecimal("2")); As you can see, without BigDecimal operator overloading, simple formulas get complicated real quick. With doubles, this looks fine, but I need the precision. I was hoping in Scala I could do this: var x = 1.1; var y = 0.1; print(x + y); And by default I would get decimal-like behaviour, alas Scala doesn't use decimal calculation by default. Then I do this in Scala: var x = BigDecimal(1.1); var y = BigDecimal(0.1); println(x + y); And I still get an imprecise result. Is there something I am not doing right in Scala? Maybe I should use Groovy to maximise readability (it uses decimals by default)?

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• system out output for double numbers in a java program

  - by Nikunj Chauhan

  I have a program where I am generating two double numbers by adding several input prices from a file based on a condition. String str; double one = 0.00; double two = 0.00; BufferedReader in = new BufferedReader(new FileReader(myFile)); while((str = in.readLine()) != null){ if(str.charAt(21) == '1'){ one += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } else{ two += Double.parseDouble(str.substring(38, 49) + "." + str.substring(49, 51)); } } in.close(); System.out.println("One: " + one); System.out.println("Two: " + two); The output is like: One: 2773554.02 Two: 6.302505836000001E7 Question: None of the input have more then two decimals in them. The way one and two are getting calculated exactly same. Then why the output format is like this. What I am expecting is: One: 2773554.02 Two: 63025058.36 Why the printing is in two different formats ? I want to write the outputs again to a file and thus there must be only two digits after decimal.

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• Decimal problem in Java

  - by Jerome

  I am experimenting with writing a java class for financial engineering (hobby of mine). The algorithm that I desire to implement is: 100 / 0.05 = 2000 Instead I get: 100 / 0.05 = 2000.9999999999998 I understand the problem to be one with converting from binary numbers to decimals (float -- int). I have looked at the BigDecimal class on the web but have not quite found what I am looking for. Attached is the program and a class that I wrote: // DCF class public class DCF { double rate; double principle; int period; public DCF(double $rate, double $principle, int $period) { rate = $rate; principle = $principle; period = $period; } // returns the console value public double consol() { return principle/rate; } // to string Method public String toString() { return "(" + rate + "," + principle + "," + period + ")"; } } Now the actual program: // consol program public class DCFmain { public static void main(String[] args) { // create new DCF DCF abacus = new DCF(0.05, 100.05, 5); System.out.println(abacus); System.out.println("Console value= " + abacus.consol() ); } } Output: (0.05,100.05,5) Console value= 2000.9999999999998 Thanks!

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