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• Question about the mathematical properties of hashes

  - by levand

  Take a commonly used binary hash function - for example, SHA-256. As the name implies, it outputs a 256 bit value. Let A be the set of all possible 256 bit binary values. A is extremely large, but finite. Let B be the set of all possible binary values. B is infinite. Let C be the set of values obtained by running SHA-256 on every member of B. Obviously this can't be done in practice, but I'm guessing we can still do mathematical analysis of it. My Question: By necessity, C ? A. But does C = A?

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 distinct colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• how many color combinations in a 24 bit image

  - by numerical25

  I am reading a book and I am not sure if its a mistake or I am misunderstanding the quote. It reads... Nowadays every PC you can buy has hardware that can render images with at least 16.7 million individual colors. Rather than have an array with thousands of color entries, the images instead contain explicit color values for each pixel. A 24-bit display, of course, uses 24 bits, or 3 bytes per pixel, for color information. This gives 1 byte, or 256 distinct values each, for red, green, and blue. This is generally called true color, because 256^3 (16.7 million) He says 1 byte is equal to 256 distinct values. 1 byte = 8 bits. 8^2 bits = 64 combinations of colors right ?? It's not adding up right to me. I know it might be something simple to understand, but I don't understand.

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• create a dataset by using modulo division method

  - by ayoom

  create a dataset with 101 integers. Use the modulo division method of hashing to store the random data values into hash tables with table sizes of 7, 51, and 151. Use the linear probing and quadratic method of collision resolution. Print out the tables after the data values have been stored. Search for 10 different values in each of the three hash tables, counting the number of comparisons necessary. Print out the number of comparisons necessary in each case, in tabular form.

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• C# string equality operator returns false, but I'm pretty sure it should be true... What?!

  - by Daniel Schaffer

  I'm trying to write a unit test for a piece of code that generates a large amount of text. I've run into an issue where the "expected" and "actual" strings appear to be equal, but Assert.AreEqual throws, and both the equality operator and Equals() return false. The result of GetHashCode() is different for both values as well. However, putting both strings into text files and comparing with DiffMerge tells me they're the same. Additionally, using Encoding.ASCII.GetBytes() on both values and then using SequenceEquals to compare the resulting byte arrays returns true. The values are 34KB each, so I'll hold off putting them here for now. Any ideas? I'm completely stumped.

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• How can I modify an Android bitmap in C++ (JNI/NDK) so that I can use on the Java side?

  - by HardCoder

  I call a C++ function over JNI and pass a RGBA_8888 bitmap, lock it, change the values, unlock it, return and then display it in Java with this C++ code: AndroidBitmap_getInfo(env, map, &info) < 0); AndroidBitmap_lockPixels(env, map, (void**)&pixel); for(i=info.width*info.height-1;i>=0;i--) { pixel[i] = 0xf1f1f1f1; } AndroidBitmap_unlockPixels(env, map); The problem I have is that the bitmaps looks not as I expect it and the pixel values (verified with getPixel) are not the same when I check them in Java from what I set them in C++. When I set the bitmap values to 0xffffffff I get the correct value in Java, but for many others I don't. 0xf1f1f1f1 for example turns into 0xF1FFFFFF. What do I have to do to make it work ? PS: I am using Android 2.3.4

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• Plotting Tweets from DB in Ruby, grouping by hour.

  - by plotti

  Hey guys I've got a couple of issues with my code. I was wondering that I am plotting the results very ineffectively, since the grouping by hour takes ages the DB is very simple it contains the tweets, created date and username. It is fed by the twitter gardenhose. Thanks for your help ! require 'rubygems' require 'sequel' require 'gnuplot' DB = Sequel.sqlite("volcano.sqlite") tweets = DB[:tweets] def get_values(keyword,tweets) my_tweets = tweets.filter(:text.like("%#{keyword}%")) r = Hash.new start = my_tweets.first[:created_at] my_tweets.each do |t| hour = ((t[:created_at]-start)/3600).round r[hour] == nil ? r[hour] = 1 : r[hour] += 1 end x = [] y = [] r.sort.each do |e| x << e[0] y << e[1] end [x,y] end keywords = ["iceland", "island", "vulkan", "volcano"] values = {} keywords.each do |k| values[k] = get_values(k,tweets) end Gnuplot.open do |gp| Gnuplot::Plot.new(gp) do |plot| plot.terminal "png" plot.output "volcano.png" plot.data = [] values.each do |k,v| plot.data << Gnuplot::DataSet.new([v[0],v[1]]){ |ds| ds.with = "linespoints" ds.title = k } end end end

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• Why I can't use template table in dynamic query SQL SERVER 2005

  - by StuffHappens

  Hello! I have the following t-sql code which generates an error Declare @table TABLE ( ID1 int, ID2 int ) INSERT INTO @table values(1, 1); INSERT INTO @table values(2, 2); INSERT INTO @table values(3, 3); DECLARE @field varchar(50); SET @field = 'ID1' DECLARE @query varchar(MAX); SET @query = 'SELECT * FROM @table WHERE ' + @field + ' = 1' EXEC (@query) The error is Must declare the table variable "@table". What's wrong with the query. How to fix it?

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• Do bit operations cause programs to run slower?

  - by flashnik

  I'm dealing with a problem which needs to work with a lot of data. Currently its values are represented as an unsigned int. I know that real values do not exceed a limit of 1000. Questions I can use unsigned short to store it. An upside to this is that it'll use less storage space to store the value. Will performance suffer? If I decided to store data as short but all the calling functions use int, it's recognized that I need to convert between these datatypes when storing or extracting values. Will performance suffer? Will the loss in performance be dramatic? If I decided to not use short but just 10 bits packed into an array of unsigned int. What will happen in this case comparing with previous ones?

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• Best way to reduce consecutive NAs to single NA

  - by digEmAll

  I need to reduce the consecutive NA's in a vector to a single NA, without touching the other values. So, for example, given a vector like this: NA NA 8 7 NA NA NA NA NA 3 3 NA -1 4 what I need to get, is the following result: NA 8 7 NA 3 3 NA -1 4 Currently, I'm using the following function: reduceConsecutiveNA2One <- function(vect){ enc <- rle(is.na(vect)) # helper func tmpFun <- function(i){ if(enc$values[i]){ data.frame(L=c(enc$lengths[i]-1, 1), V=c(TRUE,FALSE)) }else{ data.frame(L=enc$lengths[i], V=enc$values[i]) } } Df <- do.call(rbind.data.frame,lapply(1:length(enc$lengths),FUN=tmpFun)) return(vect[rep.int(!Df$V,Df$L)]) } and it seems to work fine, but probably there's a simpler/faster way to accomplish this task. Any suggestions ? Thanks in advance.

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• Need some explanation about MS Ajax using PageMethods

  - by Ahmed Said

  I have a project that uses PageMethods to call functions on the server. The server functions (written in C#) return the values as array of strings, without doing any kind of serialization and in the client side (from Js) the accessing of the return values is by using static variable called arguments. I found that sometimes for some users (cases are not repro) sometimes an exception occured "WebServiceFailedException the server method 'Foo' returned invalid data. the 'd' property is missing from JSON." Some searching on google I found that people are serializing the return values using DataContractJsonSerializer class and in js accessing the return value using one of the callback function Example: function OnRequestComplete(result, userContext, methodName) { var Person = eval('(' + result + ')'); alert(Person.Forename); alert(Person.Surname); } So is the first technique is correct? or what?

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• GNUPlot: plot different ranges with different styles

  - by Mr. Shickadance

  Hello all, I know this should be pretty simple, but I haven't been able to find a similar example. I need to plot different ranges of a datafile differently, but on the same graph. For instance, say my datafile represents a function with x and y values. I want to plot the first N values using a style like lines, and then the next M values using a different style, like points. I was thinking I would need a plot command similar to this: plot [1:5] "my.data" using 1:2 with lines, [6:12] using 1:2 with points, [13:19] using 1:2 with lines Essentially I want to distinguish different areas of the functions. Any ideas? I am sorry if it sounds like I'm rambling but I am quite stumped. Thanks in advance!

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• how do i release the auto increment serial nos that are missing

  - by mmdel

  i have a table with auto increment field and i am using transactions when inserting new data. now i find there are a few serial nos that are missing. suppose the last serial no was 475, now when i insert new row, the serial allotted to it is 481. how do i correct this. table_A fields ID(Auto increment),Name,Address table_B fields ID(Auto increment FK TO table_A ID),Tel,Fax,Email,Salesman table_C fields ID(Auto increment FK TO table_A ID),monthly_commitment mysql_query(BEGIN); $a = mysql_query("INSERT INTO table_A VALUES('','name','address')"); $b = mysql_query("INSERT INTO table_B VALUES('','tel','fax','email','salesman')"); $b = mysql_query("INSERT INTO table_C VALUES('','monthly commitment')"); if(($a) && ($b) && ($c)){mysql_query("COMMIT");} else {mysql_query("ROLLBACK");}

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• JavaScript, transform object into array

  - by Šime Vidas

  I've got an object: var obj = { "Mike": 24, "Peter": 23, "Simon": 33, "Tom": 12, "Frank": 31 }; I want to create an array that holds the values of the object. The keys (key names) can be disregarded: [24, 23, 33, 12, 31] The order of the values is NOT important! One solution (obviously) would be do have a function that takes the values and puts them into an array: var arr = valuesToArray(obj); I will accept such a function as the answer. However, I would be more pleased if there would be an API function (ECMAScript, jQuery, browser-specific, ...) that could do this. Is there such a thing?

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• infix formula in the input

  - by gcc

  input: sqrt(2 - sin(3*A/B)^2.5) + 0.5*(C*~(D) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input : sqrt(2 - asin(3*A/B)^2.5) +cos(0.5*(C*~(D)) + 3.11 +B) a b /*there are values for a,b,c,d */ c d input: sqrt(2 - sin(3*A/B)^2.5)/(0.5*(C*~(D)) + sin(3.11) +ln(B)) /*max lenght of formula is 250 characters*/ a b /*there are values for a,b,c,d */ c /*each variable with set of floating numbers*/ d As you can see infix formula in the input depends on user. My program will take a formula and n-tuples value. Then it calculate the results for each value of a,b,c and d. If you wonder I am saying ;outcome of program is graph. I dont know way how to store the formula so that I can do my job with easy. can you show me? a,b,c,d is letters cos,sin,sqrt,ln is function

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• show the list of usernames inside a div

  - by Mr_Green

  I am new to jQuery. In my project, I created one Class User in which the code is as shown below: static ConcurrentDictionary<string, User> _users = new ConcurrentDictionary<string, User>(); // // some function to add values to _users list // public List<User> GetConnectedUsers() { return _users.Values.ToList(); } I want to show this list of values in div #showUsernames. How to do this by using jQuery? I tried the below which is not showing anything /*display your contacts*/ $('#showUsernames').append(function(){ chat.server.getConnectedUsers(); }); where chat.server(signalr) calls the server-side code(Chat class).. I think the solution has nothing to do with signalr. If the above description is not enough then you can go through my code here

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• How to use SQL trigger to record the affected column's row number

  - by Freeman

  I want to have an 'updateinfo' table in order to record every update/insert/delete operations on another table. In oracle I've written this: CREATE TABLE updateinfo ( rnumber NUMBER(10), tablename VARCHAR2(100 BYTE), action VARCHAR2(100 BYTE), UPDATE_DATE date ) DROP TRIGGER TRI_TABLE; CREATE OR REPLACE TRIGGER TRI_TABLE AFTER DELETE OR INSERT OR UPDATE ON demo REFERENCING NEW AS NEW OLD AS OLD FOR EACH ROW BEGIN if inserting then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'insert',sysdate); elsif updating then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'update',sysdate); elsif deleting then insert into updateinfo(rnumber,tablename,action,update_date ) values(rownum,'demo', 'delete',sysdate); end if; -- EXCEPTION -- WHEN OTHERS THEN -- Consider logging the error and then re-raise -- RAISE; END TRI_TABLE; but when checking updateinfo, all rnumber column is zero. is there anyway to retrieve the correct row number?

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• What is the best way to "override" enums?

  - by Tyler

  I have a number of classes which extend an abstract class. The abstract parent class defines an enum with a set of values. Some of the subclasses inherit the parent class's enum values, but some of the subclasses need the enum values to be different. Is there any way to somehow override the enum for these particular subclasses, and if not, what is a good way to achieve what I'm describing? class ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { a, b, c }; } class ChildClass : ParentClass { private MyEnum m_EnumVal; public virtual MyEnum EnumVal { get { return m_EnumVal; } set { m_EnumVal = value; } } public enum MyEnum { d, e, f }; }

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• Screen orientation change forces data re-entry

  - by Timbermar

  I'm developing a simple app, only a handful of activities and nothing to complicated. The issue I'm having is that in a few of my activities I have EditText widgets, and when the screen is rotated, these widgets loose their values. They still visually, that is, on the handset screen, report their values from before the rotation, but to the code report their default values. An example, I have an activity with an EditText, I enter a number, 15, the calculator starts calculating, displays a result. If at this point I rotate to a different orientation, as expected the activity dies, reloads, shows the new orientation, my value of 15 is still in the EditText, however the calculator (the code) calculates as if it was 0, which is the initial value. I have not tried changing the initial value to see if it is really pulling from the default value, or just setting itself to 0 when I cast it as an int. If I didn't explain this well enough, let me know, I can add source code if I need to. Thanks.

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• Create new Array of parameter type

  - by pimvdb

  I'm trying to create a function to parse out all values in a multidimensional Array with all but one dimension given. The details are not relevant, but for this function I need to return an one-dimensional Array containing values of the same type the original multidimensional Array has. To pass any Array with any dimension to my function, I declared the type of this parameter as Array. However, how would I create a new Array of that specific type (e.g. Integer)? Currently I have the following code: Function GetRow(ByVal arr As Array) As Array Dim result As (...) 'This should be Integer() if arr contains Integers, etc. Return result End Function How do I declare the type of result to make it having the same type of values as arr? New Array is not possible as it is declared MustInherit. Thanks a lot.

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• Manually Building a Tree in CakePHP

  - by mabwi

  I'm currently working on building an application in CakePHP. There's a quite extensive existing data set that's conceptually a tree, but wasn't previously stored as one. What I mean by that, is there's no real relationship defined in the data. The problem I'm having is getting it to work correctly with the CakePHP tree behaviour. Because I have to set all the values on existing data - as opposed to Cake setting up the structure as elements are inserted - I need to understand how the lft/rght values work. So, I guess the question is: How does the structure data work, specifically the lft/rght values? How do I set it up so that the data comes out rationally, without inserting them one at a time? It's a 2 level tree, with Sections and sub-sections. Thanks for the help

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• Use a SELECT to Print a Bunch of INSERT INTOs

  - by Mikecancook

  I have a bunch of records I want to move to another database and I just want to create a bunch of inserts that I can copy and paste. I've seen someone do this before but I can't figure it out. I'm not getting the escapes right. It's something like this where 'Code', 'Description' and 'Absent' are the columns I want from the table. SELECT 'INSERT INTO AttendanceCodes (Code, Description, Absent) VALUES (' + Code + ',' + Description + ',' + Absent')' FROM AttendanceCodes The end result should be a slew of INSERTS with the correct values like this: INSERT INTO AttendanceCodes (Code, Description, Absent) VALUES ('A','Unverified Absence','UA')

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• Can I prevent a computed column from changing it's value if the formula changes?

  - by William Hurst

  I have a computed column in MS SQL 2005 that does some VAT calculations. The website uses invoices that can only be generated once and rely on the value in the computed column to work out the VAT. Unfortunately, a bug was found that means that the the VAT value calculated was off by a few cents. Not a huge problem but we can't change the values from all the previously computed values as these need to be honoured on the invoices. tldr; How do I change the calculation for a computed column without re-calculating the values that have already be calculated?

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• if exists, update, else insert new record

  - by I__

  i am inserting values into a table if the record exists already replace it, and if it does not exist then add a new one. so far i have this code: INSERT INTO table_name VALUES (value1, value2, value3,...) where pk="some_id"; but i need something like this if not pk="some_id" exists then INSERT INTO table_name VALUES (value1, value2, value3,...) where pk="some_id"; else update table_name where pk="some_id" what would be the correct SQL syntax for this? please note that i am using sql access and that i guess it can be a combination of vba and sql

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• Creating a New Reverse Java Array

  - by mandir08

  Given an array of ints length 3, return a new array with the elements in reverse order, so {1, 2, 3} becomes {3, 2, 1}. public int[] reverse3(int[] nums) { int[] values = new int[3]; for(int i=0; i<=nums.length-1; i++) { for(int j=nums.length-1; j>=0; j--) { values[i]=nums[j]; } } return values; } I cant get this to work properly, usually the last int in the array, becomes every single int in the new array

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