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• Rails: Design Pattern to Store Order of Relations

  - by ChrisInCambo

  Hi, I have four models: Customer, QueueRed, QueueBlue, QueueGreen. The Queue models have a one to many relationship with customers A customer must always be in a queue A customer can only be in one queue at a time A customer can change queues We must be able to find out the customers current position in their respective queue In an object model the queues would just have an array property containing customers, but ActiveRecord doesn't have arrays. In a DB I would probably create some extra tables just to handle the order of the stories in the queue. My question is what it the best way to model the relationship in ActiveRecord? Obviously there are many ways this could be done, but what is the best or the most in line with how ActiveRecord should be used? Cheers, Chris

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• C++ memory management of reference types

  - by Russel

  Hello, I'm still a fairly novice programmer and I have a question about c++ memory management with refence types. First of all, my understanding of reference types: A pointer is put on the stack and the actual data that the pointer points to is created and placed on the heap. Standard arrays and user defined classes are refence types. Is this correct? Second, my main question is do c and c++'s memory management mechanisms (malloc, free and new, delete) always handle this properly and free the memory that a class or array is pointing to? Does everything still work if those pointers get reassigned somehow to other objects of the same size/type on the heap? What if a class has a pointer member that points to another object? I am assuming that delete/freeing the class object doesn't free what it's member pointer points to, is that correct? Thanks all! -R

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• building a pairwise matrix in scipy/numpy in Python from dictionaries

  - by user248237

  I have a dictionary whose keys are strings and values are numpy arrays, e.g.: data = {'a': array([1,2,3]), 'b': array([4,5,6]), 'c': array([7,8,9])} I want to compute a statistic between all pairs of values in 'data' and build an n by x matrix that stores the result. Assume that I know the order of the keys, i.e. I have a list of "labels": labels = ['a', 'b', 'c'] What's the most efficient way to compute this matrix? I can compute the statistic for all pairs like this: result = [] for elt1, elt2 in itertools.product(labels, labels): result.append(compute_statistic(data[elt1], data[elt2])) But I want result to be a n by n matrix, corresponding to "labels" by "labels". How can I record the results as this matrix? thanks.

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• getting userbase vote average and individual user's vote in the same query?

  - by Andrew Heath

  Here goes: T1 [id] [desc] 1 lovely 2 ugly 3 slender T2 [id] [userid] [vote] 1 1 3 1 2 5 1 3 2 2 1 1 2 2 4 2 3 4 In one query (if possible) I'd like to return: T1.id, T1.desc, AVG(T2.vote), T2.vote (for user viewing the page) I can get the first 3 items with: SELECT T1.id, T1.desc, AVG(T2.vote) FROM T1 LEFT JOIN T2 ON T1.id=T2.id GROUP BY T1.id and I can get the first, second, and fourth items with: SELECT T1.id, T1.desc, T2.vote FROM T1 LEFT JOIN T2 ON T1.id=T2.id WHERE T2.userid='1' GROUP BY T1.id but I'm at a loss as to how to get all four items in one query. I tried inserting a select as the fourth term: SELECT T1.id, T1.desc, AVG(T2.vote), (SELECT T2.vote FROM T2 WHERE T2.userid='1') AS userVote etc etc but I get an error that the select returns more than one row... Help? My reason for wanting to do this in one query instead of two is that I want to be able to sort the data within MySQL rather than one it's been split into a number of arrays.

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• Unmanaged Struct Instance in Managed Class

  - by HeHasMoments

  Hi, I've got a fairly specific problem i've been struggling with for a couple of days. I'm using a native C++, one of the methods takes a ptr to a struct containing fixed size char arrays. e.g. struct userData { char data1[10]; char data2[10]; }; method: short AddItem(long id, userData* data); I'm trying to call to call this from Managed VC++ but I need to have an instance of userData I can keep hold of in my managed class. Can anyone help with how to achieve this? Thanks

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• Divide and Conquer Algo to find maximum difference between two ordered elements

  - by instance

  Given an array arr[] of integers, find out the difference between any two elements such that larger element appears after the smaller number in arr[]. Examples: If array is [2, 3, 10, 6, 4, 8, 1, 7] then returned value should be 8 (Diff between 10 and 2). If array is [ 7, 9, 5, 6, 3, 2 ] then returned value should be 2 (Diff between 7 and 9) My Algorithm: I thought of using D&C algorithm. Explanation 2, 3, 10, 6, 4, 8, 1, 7 then 2,3,10,6 and 4,8,1,7 then 2,3 and 10,6 and 4,8 and 1,7 then 2 and 3 10 and 6 4 and 8 1 and 7 Here as these elements will remain in same order, i will get the maximum difference, here it's 6. Now i will move back to merege these arrays and again find the difference between minimum of first block and maximum of second block and keep doing this till end. I am not able to implement this in my code. can anyone please provide a pseudo code for this?

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• How do you make your Java application memory efficient?

  - by Boune

  How do you optimize the heap size usage of an application that has a lot (millions) of long-lived objects? (big cache, loading lots of records from a db) Use the right data type Avoid java.lang.String to represent other data types Avoid duplicated objects Use enums if the values are known in advance Use object pools String.intern() (good idea?) Load/keep only the objects you need I am looking for general programming or Java specific answers. No funky compiler switch. Edit: Optimize the memory representation of a POJO that can appear millions of times in the heap. Use cases Load a huge csv file in memory (converted into POJOs) Use hibernate to retrieve million of records from a database Resume of answers: Use flyweight pattern Copy on write Instead of loading 10M objects with 3 properties, is it more efficient to have 3 arrays (or other data structure) of size 10M? (Could be a pain to manipulate data but if you are really short on memory...)

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• Trouble Copying custom class initialization

  - by Parad0x13

  I have a custom class of type NSObject that contains a single NSMutableArray. This class is called Mutable2DArray and is designed to emulate a 2 dimensional array of type NSMutableArray. There is a custom init method - (id)initWithX:(int)x Y:(int)y that asks for the dimensions for the array and allocates the required arrays within the only array the class owns. My issue is when I try to copy an instance of Mutable2DArray I get an error saying the copyWithZone is an unrecognized selector. I thought copy was a base method of NSObject so I'm confused why I cant create a copy of the instance like this: Mutable2DArray *Array1 = [[Mutable2DArray alloc] initWithX:10 Y:10]; Mutable2DArray *Array2 = [Array1 copy]; Am I missing something so obvious here?

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• Deep Copy using Reflection in an Extension Method for Silverlight?

  - by didibus

  So I'm trying to find a generic extension method that creates a deep copy of an object using reflection, that would work in Silverlight. Deep copy using serialization is not so great in Silverlight, since it runs in partial trust and the BinaryFormatter does not exist. I also know that reflection would be faster then serialization for cloning. It would be nice to have a method that works to copy public, private and protected fields, and is recursive so that it can copy objects in objects, and that would also be able to handle collections, arrays, etc. I have searched online, and can only find shallow copy implementations using reflection. I don't understand why, since you can just use MemberwiseClone, so to me, those implementations are useless. Thank You.

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• How to use PHP fgetcsv to create an array for each piece of data in csv file?

  - by Olivia

  I'm trying to import data from a csv file to some html code to use it in a graph I have already coded. I'm trying to use PHP and fgetcsv to create arrays for each separate piece of data to use PHP to put it into the html code. I know how to open the csv file and to print it using PHP, and how to print each separate row, but not each piece of data separated by a comma. Is there a way to do this? If this helps, this is the csv data I am trying to import. May 10,72,12,60 May 11,86,24,62 May 12,67,32,34 May 13,87,12,75 May 14,112,23,89 May 17,69,21,48 May 18,98,14,84 May 19,115,18,97 May 20,101,13,88 May 21,107,32,75 I hope that makes sense.

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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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• Send and receive Array as GET/POST using querystring

  - by Vanwaril

  I've got the following code, but it doesn't seem to work: var post_req = { array: [ [ { param1: 'something', param2: 123 } ], [ ], [ ], [ { param2: 'something', param4: 1234, param1: 'hello' } ] ] }; var data_send = querystring.stringify(post_req); var request = client.request('POST', '/', headers); request.end(data_send); and if( req.method == 'POST' ) { req.addListener('data', function(chunk) { POST = querystring.parse(chunk); console.log(POST); } } I end up with 5 sub-arrays, corresponding to the 5 parameters in the objects but with extra '][' characters in their names: { array: [ { '][param1': 'something' } , { '][param2': '123' } , { '][param2': 'something' } , { '][param4': '1234' } , { '][param1': 'hello' } ] }

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• What good practices, if any, has the agile movement lost?

  - by clarke ching

  I am a long time agile advocated but one of the things that bothers me about Agile is that a lot of agile practitioners, especially the younger ones, have thrown out or are missing a whole lot of good (non Scrum, non XP) practices. Alistair Cockburn's style of writing Use Cases springs to mind; orthogonal arrays (pairwise testing) is another. I hope this is an okay forum to ask this, but since I read mostly Agile related books and articles and work with mostly Agile folk ... is there anything I'm missing? Thanks for all your help. StackOverlow is a fantastic resource.

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• Multiplying Block Matrices in Numpy

  - by Ada Xu

  Hi Everyone I am python newbie I have to implement lasso L1 regression for a class assignment. This involves solving a quadratic equation involving block matrices. minimize x^t * H * x + f^t * x where x 0 Where H is a 2 X 2 block matrix with each element being a k dimensional matrix and x and f being a 2 X 1 vectors each element being a k dimension vector. I was thinking of using nd arrays. such that np.shape(H) = (2, 2, k, k) np.shape(x) = (2, k) But I figured out that np.dot(X, H) doesn't work here. Is there an easy way to solve this problem? Thanks in advance.

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• With javascript, is it possible to define a variable's name with another string value?

  - by Joren

  Example, I have an array called 'categories' with the value ['4','9']. I'm trying to use that value with the name of a previously defined array. I have several arrays defined earlier called row1, row2, row3 etc. I'm also using jQuery. Trying to do something like this: for (i=0; i<categories.length; i++) { row+categories[i].push($(this).attr('id')); console.log(row+categories[i]); } Obviously row+categories[i] doesn't work, but maybe gives you an idea of what I'm trying to do? In this case to push that id value onto the array 'row4' the first time it loops through and then 'row9' the second time. Thanks for your help!!

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• small string optimization for vector?

  - by BuschnicK

  I know several (all?) STL implementations implement a "small string" optimization where instead of storing the usual 3 pointers for begin, end and capacity a string will store the actual character data in the memory used for the pointers if sizeof(characters) <= sizeof(pointers). I am in a situation where I have lots of small vectors with an element size <= sizeof(pointer). I cannot use fixed size arrays, since the vectors need to be able to resize dynamically and may potentially grow quite large. However, the median (not mean) size of the vectors will only be 4-12 bytes. So a "small string" optimization adapted to vectors would be quite useful to me. Does such a thing exist? I'm thinking about rolling my own by simply brute force converting a vector to a string, i.e. providing a vector interface to a string. Good idea?

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• .net Compiler Optimizations

  - by Dested

  I am writing an application that I need to run at incredibly low speeds. The application creates and destroys memory in creative ways throughout its run, and it works just fine. I am wondering what compiler optimizations occur so I can try to build to that. One trick off hand is that the CLR handles arrays much faster than lists, so if you need to handle a ton of elements in a List, you may be better off calling ToArray() and handling it rather than calling ElementAt() again and again. I am wondering if there is any sort of comprehensive list for this kind of thing, or maybe the SO community can create one :-)

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• how to get the individual parameters from the list of dynamic parameters in a webmethod,sent using

  - by kranthi

  hi, I am using jquery ajax method on my aspx page,which will invoke the webmethod in the code behind.Currently the webmethod takes a couple of parameters like firstname,lastname,address etc which I am passing from jquery ajax method using data:JSON.stringify({fname:firstname,lname:lastname,city:city}) now my requirement has been changed such that,the number and type of parameters that are going to be passed is not fixed for ex.parameter combination can be something like fname,city or fname,city or city,lname or fname,lname,city or something else.So the webmethod should be such that it should accept any number parameters.I thought of using arrays to do so, as described here. But I do not understand how can I identify which and how many parameters have been passed to the webmethod to insert/update the data to the DB.Please could someone help me with this? thanks

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• ASP.NET C# Application Object Getters and Setters

  - by kellax

  I have had a hard time finiding a newbie friendly example of accessing Application Object. I have few things ( arrays ) i would like to store in Application Object to keep as persistant data for about 2h till AppRecycle Anyhow i know how to set an Application Object variable this way: // One way String[] users = new String[1000]; Application["users"] = users; // Another way Application.Add("users", users); However i do not know how to access these variables once in Application Object there is a Getter method Get however it requires int index and other one Contents which get's everything. Here i try to retrive my String[] array but gives me a error that i am trying to convert Object to String. String[] usersTable = Application["users"]; // Since this is an object i also tried Application.users but gives error

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• jQuery version of YAHOO.lang (isUndefined, isNull, isString etc.)

  - by Chris S

  Does anyone know of a jQuery plugin that has 'helpers' or extensions like those found in the YAHOO.lang namespace? I have in mind functions such as: isNull isDefined isString isFunction I would also appreciate the same kind of thing for strings and arrays, such as Contains, StartsWith (I know these are easy to write, I'm just looking for a plugin that encompasses them all). It's not in the YAHOO.lang namespace but also form related extensions- determining a radiobox's value (from the one checked), a form element's type in a friendly name. Specifically a plugin with fluent API rather than selector based such as $("input[@type=radio][@checked]") Again I'm aware they're easy to implement but I don't want to reinvent the wheel.

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• reading a line, tokenizing and assigning to struct in C

  - by Dervin Thunk

  line is fgets'd, and running in a while loop with counter n, d is a struct with 2 char arrays, p and q. Basically, in a few words, I want to read a line, separate it into 2 strings, one up until the first space, and the rest of the line. I clean up afterwards (\n from the file becomes \'0'). The code works, but is there a more idiomatic way to do this? What errors am I running into "unknowingly"? int spc = strcspn(line," "); strncpy(d[n].p, line, spc); d[n].p[spc+1]='\0'; int l = strlen(line)-spc; strncpy(d[n].q, line+spc+1, l); char* nl = strchr(d[n].q, '\n'); if(nl){ *nl='\0'; } n++; Thanks.

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• How can this code be made more Pythonic?

  - by usethedeathstar

  This next part of code does exactly what I want it to do. dem_rows and dem_cols contain float values for a number of things i can identify in an image, but i need to get the nearest pixel for each of them, and than to make sure I only get the unique points, and no duplicates. The problem is that this code is ugly and as far as I get it, as unpythonic as it gets. If there would be a pure-numpy-solution (without for-loops) that would be even better. # next part is to make sure that we get the rounding done correctly, and than to get the integer part out of it # without the annoying floatingpoint-error, and without duplicates fielddic={} for i in range(len(dem_rows)): # here comes the ugly part: abusing the fact that i overwrite dictionary keys if I get duplicates fielddic[int(round(dem_rows[i]) + 0.1), int(round(dem_cols[i]) + 0.1)] = None # also very ugly: to make two arrays of integers out of the first and second part of the keys field_rows = numpy.zeros((len(fielddic.keys())), int) field_cols = numpy.zeros((len(fielddic.keys())), int) for i, (r, c) in enumerate(fielddic.keys()): field_rows[i] = r field_cols[i] = c

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• loading Data in VBA from a text file

  - by omegayen

  I am not very familiar with VBA but need to use it for a new software program I am using (not Microsoft related) I have a text file that has columns of data I would like to read into VBA. Specifically the text file has 4 entries per row. Thus I would like to load in the column vectors (N by 1). The text file is separated by a space between each entry. So for example I want to load in column one and save it as array A, then column two and save as array B, then column three and save as array C, and then column four and save as array D. This code snippet found below from http://www.tek-tips.com/faqs.cfm?fid=482 is something I found that can load in text to an array, but I need to adapt it to be able to save the columns as different arrays as specified above... Open "MyFile.txt" For Input As #1 ReDim Txt$(0) Do While Not EOF(1) ReDim Preserve Txt$(UBound(Txt$) + 1) Input #1, Txt$(UBound(Txt$)) Loop Close #1

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• Algorithm to find added/removed elements in an array

  - by jj

  Hi all, I am looking for the most efficent way of solving the following Problem: given an array Before = { 8, 7, 2, 1} and an array After ={1, 3, 8, 8} find the added and the removed elements the solution is: added = 3, 8 removed = 7, 2, 1 My idea so far is: for i = 0 .. B.Lenghtt-1 { for j= 0 .. A.Lenght-1 { if A[j] == B[i] A[j] = 0; B[i] = 0; break; } } // B elemnts different from 0 are the Removed elements // A elemnts different from 0 are the Added elemnts Does anyone know a better solution perhaps more efficent and that doesn't overwrite the original arrays

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• How do you find the last element of an array while iterating using a foreach loop in php ?

  - by Vaibhav Kamble

  I am writing a sql query creator using some parameters. While doing that ,I came across this problem. In java , Its very easy to detect the last element of an array from inside the for loop by just checking the current array position with the array length. for(int i=0; i< arr.length;i++){ boolean isLastElem = i== (arr.length -1) ? true : false; } php has some different fashion. They have non integer indexes to access arrays. So you must iterate over an array using foreach loop. But it becomes very problematic when you need to take some decision (in my case to append or/and parameter while building query). I am sure there must be some standard way of doing this. How do you solve this problem normally in php ?

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