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• Cannot iterate of a collection of Anonymous Types created from a LINQ Query in VB.NET

  - by Atari2600

  Ok everyone, I must be missing something here. Every LINQ example I have seen for VB.NET anonymous types claims I can do something like this: Dim Info As EnumerableRowCollection = pDataSet.Tables(0).AsEnumerable Dim Infos = From a In Info _ Select New With {.Prop1 = a("Prop1"), .Prop2 = a("Prop2"), .Prop3 = a("Prop3") } Now when I go to iterate through the collection(see example below), I get an error that says "Name "x" is not declared. For Each x in Infos ... Next It's like VB.NET doesn't understand that Infos is a collection of anonymous types created by LINQ and wants me to declare "x" as some type. (Wouldn't this defeat the purpose of an anonymous type?) I have added the references to System.Data.Linq and System.Data.DataSetExtensions to my project. Here is what I am importing with the class: Imports System.Linq Imports System.Linq.Enumerable Imports System.Linq.Queryable Imports System.Data.Linq Any ideas?

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• How to iterate through a Hash in Ruby ?

  - by Big Bang Theory

  Hi I would like to iterate @some_value outputs the following result {"Meta"=>{"Query"=>"java", "ResultOffset"=>"1", "NumResults"=>"1", "TotalResults"=>"21931"}} i need to retrieve the Value of each individual value for example java 1 1 21931

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• BASH statements execute alone but return "no such file" in for loop.

  - by reve_etrange

  Another one I can't find an answer for, and it feels like I've gone mad. I have a BASH script using a for loop to run a complex command (many protein sequence alignments) on a lot of files (~5000). The loop produces statements that will execute when given alone (i.e. copy-pasted from the error message to the command prompt), but which return "no such file or directory" inside the loop. Script below; there are actually several more arguments but this includes some representative ones and the file arguments. #!/bin/bash # Pass directory with targets as FASTA sequences as argument. # Arguments to psiblast # Common db=local/db/nr/nr outfile="/mnt/scratch/psi-blast" e=0.001 threads=8 itnum=5 pssm="/mnt/scratch/psi-blast/pssm." pssm_txt="/mnt/scratch/psi-blast/pssm." pseudo=0 pwa_inclusion=0.002 for i in ${1}/* do filename=$(basename $i) "local/ncbi-blast-2.2.23+/bin/psiblast\ -query ${i}\ -db $db\ -out ${outfile}/${filename}.out\ -evalue $e\ -num_threads $threads\ -num_iterations $itnum\ -out_pssm ${pssm}$filename\ -out_ascii_pssm ${pssm_txt}${filename}.txt\ -pseudocount $pseudo\ -inclusion_ethresh $pwa_inclusion" done Running this scripts gives "<scriptname> line <last line before 'done'>: <attempted command> : No such file or directory. If I then paste the attempted command onto the prompt it will run. Each of these commands takes a couple of minutes to run.

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• How do I iterate over the properties of an anonymous object in C#?

  - by Tomas Lycken

  I want to take an anonymous object as argument to a method, and then iterate over its properties to add each property/value to a a dynamic ExpandoObject. So what I need is to go from new { Prop1 = "first value", Prop2 = SomeObjectInstance, Prop3 = 1234 } to knowing names and values of each property, and being able to add them to the ExpandoObject. How do I accomplish this? Side note: This will be done in many of my unit tests (I'm using it to refactor away a lot of junk in the setup), so performance is to some extent relevant. I don't know enough about reflection to say for sure, but from what I've understood it's pretty performance heavy, so if it's possible I'd rather avoid it... Follow-up question: As I said, I'm taking this anonymous object as an argument to a method. What datatype should I use in the method's signature? Will all properties be available if I use object?

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• f# iterating over two arrays, using function from a c# library

  - by user343550

  I have a list of words and a list of associated part of speech tags. I want to iterate over both, simultaneously (matched index) using each indexed tuple as input to a .NET function. Is this the best way (it works, but doesn't feel natural to me): let taggingModel = SeqLabeler.loadModel(lthPath + "models\penn_00_18_split_dict.model"); let lemmatizer = new Lemmatizer(lthPath + "v_n_a.txt") let input = "the rain in spain falls on the plain" let words = Preprocessor.tokenizeSentence( input ) let tags = SeqLabeler.tagSentence( taggingModel, words ) let lemmas = Array.map2 (fun x y -> lemmatizer.lookup(x,y)) words tags

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• How to execute T-SQL for several databases which names are stored on a table

  - by emzero

  Hey guys, so here's the deal. I have several databases (SqlServer 2005) on the same server with the same schema but different data. I have one extra database which has one table storing the names of the mentioned databases. So what I need to do is to iterate over those databases name and actually "switch" to each one (use [dbname]) and execute a T-SQL script. Am I clear? Let me give you an example (simplified from the real one): CREATE TABLE DatabaseNames ( Id int, Name varchar(50) ) INSERT INTO DatabaseNames SELECT 'DatabaseA' INSERT INTO DatabaseNames SELECT 'DatabaseB' INSERT INTO DatabaseNames SELECT 'DatabaseC' Assume that DatabaseA, DatabaseB and DatabaseC are real existing databases. So let's say I need to create a new SP on those DBs. I need some script that loops over those databases and executes the T-SQL script I specify (maybe stored on a varchar variable or wherever). Any ideas? Thanks!

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• C# acting weird when reading in values from a file to an array

  - by Whitey

  This is the structure of my file: 1111111111111111111111111 2222222222222222222222222 3333333333333333333333333 4444444444444444444444444 5555555555555555555555555 6666666666666666666666666 7777777777777777777777777 8888888888888888888888888 9999999999999999999999999 0000000000000000000000000 0000000000000000000000000 0000000000000000000000000 0000000000000000000000000 0000000000000000000000000 And this is the code I'm using to read it into an array: using (StreamReader reader = new StreamReader(mapPath)) { string line; for (int i = 0; i < iMapHeight; i++) { if ((line = reader.ReadLine()) != null) { for (int j = 0; j < iMapWidth; j++) { iMap[i, j] = line[j]; } } } } I have done some debugging, and line[j] correctly iterates through each character in the currently read line. The problem lies with iMap[i, j]. After this block of code executes, this is the contents of iMap: - iMap {int[14, 25]} int[,] [0, 0] 49 int [0, 1] 49 int [0, 2] 49 int [0, 3] 49 int [0, 4] 49 int [0, 5] 49 int [0, 6] 49 int [0, 7] 49 int [0, 8] 49 int [0, 9] 49 int [0, 10] 49 int [0, 11] 49 int [0, 12] 49 int [0, 13] 49 int [0, 14] 49 int [0, 15] 49 int [0, 16] 49 int [0, 17] 49 int [0, 18] 49 int [0, 19] 49 int [0, 20] 49 int [0, 21] 49 int [0, 22] 49 int [0, 23] 49 int [0, 24] 49 int [1, 0] 50 int [1, 1] 50 int [1, 2] 50 int [1, 3] 50 int [1, 4] 50 int [1, 5] 50 int [1, 6] 50 int [1, 7] 50 int [1, 8] 50 int [1, 9] 50 int [1, 10] 50 int [1, 11] 50 int [1, 12] 50 int [1, 13] 50 int [1, 14] 50 int [1, 15] 50 int [1, 16] 50 int [1, 17] 50 int [1, 18] 50 int [1, 19] 50 int [1, 20] 50 int [1, 21] 50 int [1, 22] 50 int [1, 23] 50 int [1, 24] 50 int [2, 0] 51 int [2, 1] 51 int [2, 2] 51 int [2, 3] 51 int [2, 4] 51 int [2, 5] 51 int [2, 6] 51 int [2, 7] 51 int [2, 8] 51 int [2, 9] 51 int [2, 10] 51 int [2, 11] 51 int [2, 12] 51 int [2, 13] 51 int [2, 14] 51 int [2, 15] 51 int [2, 16] 51 int [2, 17] 51 int [2, 18] 51 int [2, 19] 51 int [2, 20] 51 int [2, 21] 51 int [2, 22] 51 int [2, 23] 51 int [2, 24] 51 int [3, 0] 52 int [3, 1] 52 int [3, 2] 52 int [3, 3] 52 int [3, 4] 52 int [3, 5] 52 int [3, 6] 52 int [3, 7] 52 int [3, 8] 52 int [3, 9] 52 int [3, 10] 52 int [3, 11] 52 int [3, 12] 52 int [3, 13] 52 int [3, 14] 52 int [3, 15] 52 int [3, 16] 52 int [3, 17] 52 int [3, 18] 52 int [3, 19] 52 int [3, 20] 52 int [3, 21] 52 int [3, 22] 52 int [3, 23] 52 int [3, 24] 52 int [4, 0] 53 int [4, 1] 53 int [4, 2] 53 int [4, 3] 53 int [4, 4] 53 int [4, 5] 53 int [4, 6] 53 int [4, 7] 53 int [4, 8] 53 int [4, 9] 53 int [4, 10] 53 int [4, 11] 53 int [4, 12] 53 int [4, 13] 53 int [4, 14] 53 int [4, 15] 53 int [4, 16] 53 int [4, 17] 53 int [4, 18] 53 int [4, 19] 53 int [4, 20] 53 int [4, 21] 53 int [4, 22] 53 int [4, 23] 53 int [4, 24] 53 int [5, 0] 54 int [5, 1] 54 int [5, 2] 54 int [5, 3] 54 int [5, 4] 54 int [5, 5] 54 int [5, 6] 54 int [5, 7] 54 int [5, 8] 54 int [5, 9] 54 int [5, 10] 54 int [5, 11] 54 int [5, 12] 54 int [5, 13] 54 int [5, 14] 54 int [5, 15] 54 int [5, 16] 54 int [5, 17] 54 int [5, 18] 54 int [5, 19] 54 int [5, 20] 54 int [5, 21] 54 int [5, 22] 54 int [5, 23] 54 int [5, 24] 54 int [6, 0] 55 int [6, 1] 55 int [6, 2] 55 int [6, 3] 55 int [6, 4] 55 int [6, 5] 55 int [6, 6] 55 int [6, 7] 55 int [6, 8] 55 int [6, 9] 55 int [6, 10] 55 int [6, 11] 55 int [6, 12] 55 int [6, 13] 55 int [6, 14] 55 int [6, 15] 55 int [6, 16] 55 int [6, 17] 55 int [6, 18] 55 int [6, 19] 55 int [6, 20] 55 int [6, 21] 55 int [6, 22] 55 int [6, 23] 55 int [6, 24] 55 int [7, 0] 56 int [7, 1] 56 int [7, 2] 56 int [7, 3] 56 int [7, 4] 56 int [7, 5] 56 int [7, 6] 56 int [7, 7] 56 int [7, 8] 56 int [7, 9] 56 int [7, 10] 56 int [7, 11] 56 int [7, 12] 56 int [7, 13] 56 int [7, 14] 56 int [7, 15] 56 int [7, 16] 56 int [7, 17] 56 int [7, 18] 56 int [7, 19] 56 int [7, 20] 56 int [7, 21] 56 int [7, 22] 56 int [7, 23] 56 int [7, 24] 56 int [8, 0] 57 int [8, 1] 57 int [8, 2] 57 int [8, 3] 57 int [8, 4] 57 int [8, 5] 57 int [8, 6] 57 int [8, 7] 57 int [8, 8] 57 int [8, 9] 57 int [8, 10] 57 int [8, 11] 57 int [8, 12] 57 int [8, 13] 57 int [8, 14] 57 int [8, 15] 57 int [8, 16] 57 int [8, 17] 57 int [8, 18] 57 int [8, 19] 57 int [8, 20] 57 int [8, 21] 57 int [8, 22] 57 int [8, 23] 57 int [8, 24] 57 int [9, 0] 48 int [9, 1] 48 int [9, 2] 48 int [9, 3] 48 int [9, 4] 48 int [9, 5] 48 int [9, 6] 48 int [9, 7] 48 int [9, 8] 48 int [9, 9] 48 int [9, 10] 48 int [9, 11] 48 int [9, 12] 48 int [9, 13] 48 int [9, 14] 48 int [9, 15] 48 int [9, 16] 48 int [9, 17] 48 int [9, 18] 48 int [9, 19] 48 int [9, 20] 48 int [9, 21] 48 int [9, 22] 48 int [9, 23] 48 int [9, 24] 48 int [10, 0] 48 int [10, 1] 48 int [10, 2] 48 int [10, 3] 48 int [10, 4] 48 int [10, 5] 48 int [10, 6] 48 int [10, 7] 48 int [10, 8] 48 int [10, 9] 48 int [10, 10] 48 int [10, 11] 48 int [10, 12] 48 int [10, 13] 48 int [10, 14] 48 int [10, 15] 48 int [10, 16] 48 int [10, 17] 48 int [10, 18] 48 int [10, 19] 48 int [10, 20] 48 int [10, 21] 48 int [10, 22] 48 int [10, 23] 48 int [10, 24] 48 int [11, 0] 48 int [11, 1] 48 int [11, 2] 48 int [11, 3] 48 int [11, 4] 48 int [11, 5] 48 int [11, 6] 48 int [11, 7] 48 int [11, 8] 48 int [11, 9] 48 int [11, 10] 48 int [11, 11] 48 int [11, 12] 48 int [11, 13] 48 int [11, 14] 48 int [11, 15] 48 int [11, 16] 48 int [11, 17] 48 int [11, 18] 48 int [11, 19] 48 int [11, 20] 48 int [11, 21] 48 int [11, 22] 48 int [11, 23] 48 int [11, 24] 48 int [12, 0] 48 int [12, 1] 48 int [12, 2] 48 int [12, 3] 48 int [12, 4] 48 int [12, 5] 48 int [12, 6] 48 int [12, 7] 48 int [12, 8] 48 int [12, 9] 48 int [12, 10] 48 int [12, 11] 48 int [12, 12] 48 int [12, 13] 48 int [12, 14] 48 int [12, 15] 48 int [12, 16] 48 int [12, 17] 48 int [12, 18] 48 int [12, 19] 48 int [12, 20] 48 int [12, 21] 48 int [12, 22] 48 int [12, 23] 48 int [12, 24] 48 int [13, 0] 48 int [13, 1] 48 int [13, 2] 48 int [13, 3] 48 int [13, 4] 48 int [13, 5] 48 int [13, 6] 48 int [13, 7] 48 int [13, 8] 48 int [13, 9] 48 int [13, 10] 48 int [13, 11] 48 int [13, 12] 48 int [13, 13] 48 int [13, 14] 48 int [13, 15] 48 int [13, 16] 48 int [13, 17] 48 int [13, 18] 48 int [13, 19] 48 int [13, 20] 48 int [13, 21] 48 int [13, 22] 48 int [13, 23] 48 int [13, 24] 48 int Sorry for the lame formatting, but it's huge :P I have no idea where it's getting these values from, does anyone have an explanation? Thanks :)

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• Codeigniter: Make field increase by 1 up to a number?

  - by Kevin Brown

  In my validation class I have this: $fields['a_1'] = 'First Question'; $fields['a_2'] = 'Second Question'; $fields['a_3'] = 'Third Question'; $fields['a_4'] = 'Fourth Question'; This is getting old--I have about 40 of these to write, and each set has matching validation rules: $rules['a_1'] = 'hour'; $rules['a_2'] = 'hour'; ... Is there a way to say: $fields['a_' . 1 - 17] = "One, Two" Etc... Just curious... if not, I'll brute force it.

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• More advanced usage of interfaces

  - by owca

  To be honest I'm not quite sure if I understand the task myself :) I was told to create class MySimpleIt, that implements Iterator and Iterable and will allow to run the provided test code. Arguments and variables of objects cannot be either Collections or arrays. The code : MySimpleIt msi=new MySimple(10,100, MySimpleIt.PRIME_NUMBERS); for(int el: msi) System.out.print(el+" "); System.out.println(); msi.setType(MySimpleIterator.ODD_NUMBERS); msi.setLimits(15,30); for(int el: msi) System.out.print(el+" "); System.out.println(); msi.setType(MySimpleIterator.EVEN_NUMBERS); for(int el: msi) System.out.print(el+" "); System.out.println(); The result I should obtain : 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 15 17 19 21 23 25 27 29 16 18 20 22 24 26 28 30 And here's my code : import java.util.Iterator; interface MySimpleIterator{ static int ODD_NUMBERS=0; static int EVEN_NUMBERS = 1; static int PRIME_NUMBERS = 2; int setType(int i); } public class MySimpleIt implements Iterable, Iterator, MySimpleIterator { public MySimple my; public MySimpleIt(MySimple m){ my = m; } public int setType(int i){ my.numbers = i; return my.numbers; } public void setLimits(int d, int u){ my.down = d; my.up = u; } public Iterator iterator(){ Iterator it = this.iterator(); return it; } public void remove(){ } public Object next(){ Object o = new Object(); return o; } public boolean hasNext(){ return true; } } class MySimple { public int down; public int up; public int numbers; public MySimple(int d, int u, int n){ down = d; up = u; numbers = n; } } In the test code I have error in line when creating MySimpleIt msi object, as it finds MySimple instead of MySimpleIt. Also I have errors in for-each loops, because compiler wants 'ints' there instead of Object. Anyone has any idea on how to solve it ?

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• Iterating over two dimension array and knowing current position

  - by Nuno Furtado

  I am trying to iterate a multidimension array created with the following line To iterate i'm using the following code visiblematrix= Array.new (10) {Array.new(10){0}} But this doesn't allow me to know the current x,y position while iterating. how can i find it out without resorting to temporary variables visiblematrix.each do |x| x.each do |y| puts y end end

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• How to execute T-SQL for several databases whose names are stored in a table

  - by emzero

  Hey guys, so here's the deal. I have several databases (SqlServer 2005) on the same server with the same schema but different data. I have one extra database which has one table storing the names of the mentioned databases. So what I need to do is to iterate over those databases name and actually "switch" to each one (use [dbname]) and execute a T-SQL script. Am I clear? Let me give you an example (simplified from the real one): CREATE TABLE DatabaseNames ( Id int, Name varchar(50) ) INSERT INTO DatabaseNames SELECT 'DatabaseA' INSERT INTO DatabaseNames SELECT 'DatabaseB' INSERT INTO DatabaseNames SELECT 'DatabaseC' Assume that DatabaseA, DatabaseB and DatabaseC are real existing databases. So let's say I need to create a new SP on those DBs. I need some script that loops over those databases and executes the T-SQL script I specify (maybe stored on a varchar variable or wherever). Any ideas? Thanks!

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• How do I use Python's itertools.groupby()?

  - by James Sulak

  I haven't been able to find an understandable explanation of how to actually use Python's itertools.groupby() function. What I'm trying to do is this: take a list - in this case, the children of an objectified lxml element - divide it into groups based on some criteria, and then later iterate over each of these groups separately. I've reviewed the documentation (http://docs.python.org/lib/itertools-functions.html), and the examples, (http://docs.python.org/lib/itertools-example.html), but I've had trouble trying to apply them beyond a simple list of numbers. So, how do I use of itertools.groupby()? Is there another technique I should be using? Pointers to good "prerequisite" reading would also be appreciated.

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• iterate through fb:random

  - by fusion

  does anyone know how i would fill data from mysql database in fb:random and iterate through it, to pick a random quote? fb:random $facebook->api_client->fbml_setRefHandle('quotes', '<fb:random> <fb:random-option>Quote 1</fb:random-option> <fb:random-option>Quote 2</fb:random-option> </fb:random>'); mysql data: $rowcount = mysql_result($result, 0, 0); $rand = rand(0,$rowcount-1); $result = mysql_query("SELECT cQuotes, vAuthor, cArabic, vReference FROM thquotes LIMIT $rand, 1", $conn) or die ('Error: '.mysql_error()); $row = mysql_fetch_array($result, MYSQL_ASSOC); if ( !$row ) { echo "Empty"; } else{ $fb_box = "<p>" . h($row['cArabic']) . "</p>"; $fb_box .= "<p>" . h($row['cQuotes']) . "</p>"; $fb_box .= "<p>" . h($row['vAuthor']) . "</p>"; $fb_box .= "<p>" . h($row['vReference']) . "</p>"; }

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• Overlapping matches with finditer() in Python

  - by Raphink

  Hi there, I'm using a regex to match Bible verse references in a text. The current regex is REF_REGEX = re.compile(r'(?<!\w)((?i)q(?:uote)?\s+)?((?:(?:[1-3]|I{1,3})\s*)?[A-Za-z]+)\.?(?:\s*(\d+)(?:[:.](\d+)(?:-(\d+))?)?)(?:\s+(?:(?i)(?:from\s+)|(?:in\s+)|(?P<lbrace>\())\s*(\w+)(?(lbrace)\)))?', re.UNICODE) This matches the following expressions fine: "jn 3:16": (None, 'jn', '3', '16', None, None, None), "matt. 18:21-22": (None, 'matt', '18', '21', '22', None, None), "q matt. 18:21-22": ('q ', 'matt', '18', '21', '22', None, None), "QuOTe jn 3:16": ('QuOTe ', 'jn', '3', '16', None, None, None), "q 1co13:1": ('q ', '1co', '13', '1', None, None, None), "q 1 co 13:1": ('q ', '1 co', '13', '1', None, None, None), "quote 1 co 13:1": ('quote ', '1 co', '13', '1', None, None, None), "quote 1co13:1": ('quote ', '1co', '13', '1', None, None, None), "jean 3:18 (PDV)": (None, 'jean', '3', '18', None, '(', 'PDV'), "quote malachie 1.1-2 fRom Colombe": ('quote ', 'malachie', '1', '1', '2', None, 'Colombe'), "quote malachie 1.1-2 In Colombe": ('quote ', 'malachie', '1', '1', '2', None, 'Colombe'), "cinq jn 3:16 (test)": (None, 'jn', '3', '16', None, '(', 'test'), "Q IIKings5.13-58 from wolof": ('Q ', 'IIKings', '5', '13', '58', None, 'wolof'), "This text is about lv5.4-6 in KJV only": (None, 'lv', '5', '4', '6', None, 'KJV'), but it fails to parse: "Found in 2 Cor. 5:18-21 ( Ministers": (None, '2 Cor', '5', '18', '21', None, None), because it returns (None, 'in', '2', None, None, None, None) instead. Is there a way to get finditer() to return all matches, even if they overlap, or is there a way to improve my regex so it matches this last bit properly? Thanks.

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• Bash: Correct way to Iterate over Map

  - by Lars Tackmann

  In Bash I can create a map (hashtable) with this common construction hput() { eval "$1""$2"='$3' } hget() { eval echo '${'"$1$2"'#hash}' } and then use it like this: hput capitols France Paris hput capitols Spain Madrid echo "$(hget capitols France)" But how do I best iterate over the entries in the map ?. For instance, in Java I would do: for (Map.Entry<String, String> entry : capitols.entrySet()) { System.out.println("Country " + entry.getKey() + " capital " + entry.getValue()); } is there a common way of accomplishing something similar in Bash ?.

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• Python list comprehension to return edge values of a list

  - by mvid

  If I have a list in python such as: stuff = [1, 2, 3, 4, 5, 6, 7, 8, 9] with length n (in this case 9) and I am interested in creating lists of length n/2 (in this case 4). I want all possible sets of n/2 values in the original list, for example: [1, 2, 3, 4], [2, 3, 4, 5], ..., [9, 1, 2, 3] is there some list comprehension code I could use to iterate through the list and retrieve all of those sublists? I don't care about the order of the values within the lists, I am just trying to find a clever method of generating the lists.

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• Iterate through main function in C?

  - by Mohit Deshpande

  Here is my main function: int main(int argc, char **argv) { LoadFile(); Node *temp; char *key; switch (GetUserInput()) { case 1: temp = malloc(sizeof(Node)); printf("\nEnter the key of the new node: "); scanf("%s", temp->key); printf("\nEnter the value of the new node: "); scanf("%s", temp->value); AddNode(temp); free(temp); break; case 2: key = malloc(sizeof(char *)); printf("Enter the key of the node you want to delete: "); scanf("%s", key); DeleteNode(key); free(key); break; case 3: PrintAll(); break; case 4: SaveFile(); break; case 5: return 0; break; default: printf("\nWrong choice!\n"); break; } return 0; } The only problem with it is that after any case statement breaks, the program just exits out. I understand why, but I don't know how to fix it. I want the program to repeat itself each time even after the case statements. Would I just say: main(argc, argv); before every break statement?

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• Python: Memory usage and optimization when modifying lists

  - by xApple

  The problem My concern is the following: I am storing a relativity large dataset in a classical python list and in order to process the data I must iterate over the list several times, perform some operations on the elements, and often pop an item out of the list. It seems that deleting one item out of a Python list costs O(N) since Python has to copy all the items above the element at hand down one place. Furthermore, since the number of items to delete is approximately proportional to the number of elements in the list this results in an O(N^2) algorithm. I am hoping to find a solution that is cost effective (time and memory-wise). I have studied what I could find on the internet and have summarized my different options below. Which one is the best candidate ? Keeping a local index: while processingdata: index = 0 while index < len(somelist): item = somelist[index] dosomestuff(item) if somecondition(item): del somelist[index] else: index += 1 This is the original solution I came up with. Not only is this not very elegant, but I am hoping there is better way to do it that remains time and memory efficient. Walking the list backwards: while processingdata: for i in xrange(len(somelist) - 1, -1, -1): dosomestuff(item) if somecondition(somelist, i): somelist.pop(i) This avoids incrementing an index variable but ultimately has the same cost as the original version. It also breaks the logic of dosomestuff(item) that wishes to process them in the same order as they appear in the original list. Making a new list: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) newlist = [] for item in somelist: if somecondition(item): newlist.append(item) somelist = newlist gc.collect() This is a very naive strategy for eliminating elements from a list and requires lots of memory since an almost full copy of the list must be made. Using list comprehensions: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist[:] = [x for x in somelist if somecondition(x)] This is very elegant but under-the-cover it walks the whole list one more time and must copy most of the elements in it. My intuition is that this operation probably costs more than the original del statement at least memory wise. Keep in mind that somelist can be huge and that any solution that will iterate through it only once per run will probably always win. Using the filter function: while processingdata: for i, item in enumerate(somelist): dosomestuff(item) somelist = filter(lambda x: not subtle_condition(x), somelist) This also creates a new list occupying lots of RAM. Using the itertools' filter function: from itertools import ifilterfalse while processingdata: for item in itertools.ifilterfalse(somecondtion, somelist): dosomestuff(item) This version of the filter call does not create a new list but will not call dosomestuff on every item breaking the logic of the algorithm. I am including this example only for the purpose of creating an exhaustive list. Moving items up the list while walking while processingdata: index = 0 for item in somelist: dosomestuff(item) if not somecondition(item): somelist[index] = item index += 1 del somelist[index:] This is a subtle method that seems cost effective. I think it will move each item (or the pointer to each item ?) exactly once resulting in an O(N) algorithm. Finally, I hope Python will be intelligent enough to resize the list at the end without allocating memory for a new copy of the list. Not sure though. Abandoning Python lists: class Doubly_Linked_List: def __init__(self): self.first = None self.last = None self.n = 0 def __len__(self): return self.n def __iter__(self): return DLLIter(self) def iterator(self): return self.__iter__() def append(self, x): x = DLLElement(x) x.next = None if self.last is None: x.prev = None self.last = x self.first = x self.n = 1 else: x.prev = self.last x.prev.next = x self.last = x self.n += 1 class DLLElement: def __init__(self, x): self.next = None self.data = x self.prev = None class DLLIter: etc... This type of object resembles a python list in a limited way. However, deletion of an element is guaranteed O(1). I would not like to go here since this would require massive amounts of code refactoring almost everywhere.

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• Recursive vs. Iterative algorithms

  - by teehoo

  I'm implementing the Euclidian algorithm for finding the GCD (Greatest Common Divisor) of two integers. Two sample implementations are given: Recursive and Iterative. http://en.wikipedia.org/wiki/Euclidean_algorithm#Implementations My Question: In school I remember my professors talking about recursive functions like they were all the rage, but I have one doubt. Compared to an iterative version don't recursive algorithms take up more stack space and therefore much more memory? Also, because calling a function requires uses some overhead for initialization, aren't recursive algorithms more slower than their iterative counterpart?

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• Python: Remove items from a list while iterating in Python

  - by xApple

  My problem is simple: I have a long list of elements that I want to iterate through and check every element against a condition. Depending on the outcome of the condition I would like to delete the current element of the list, and continue iterating over it as usual. I have read a few other threads on this matter. Two solutions seam to be proposed. Either make a dictionary out of the list (which implies making a copy of all the data that is already filling all the RAM in my case). Either walk the list in reverse (which breaks the concept of the alogrithm I want to implement). Is there any better or more elegant way than this to do it ? def walk_list(list_of_g): g_index = 0 while g_index < len(list_of_g): g_current = list_of_g[g_index] if subtle_condition(g_current): list_of_g.pop(g_index) else: g_index = g_index + 1

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• Is there a way to increase performance on my simple textfilter?

  - by djerry

  Hey guys, I'm writing a filter that will pick out items. I have a list of Objects. The objects contain a number, name and some other irrelevant items. At the moment, the list contains 200 items. When typing in a textbox, i'm looking if the string matches a part of the number/name of the objects in the list. If so, add them to the listbox. Here's the code for my textbox textchanged event : private void txtTelnumber_TextChanged(object sender, TextChangedEventArgs e) { lstOverview.Items.Clear(); string data = ""; foreach (ucTelListItem telList in _allUsers) { data = telList.User.H323 + telList.user.E164; if (data.Contains(txtTelnumber.Text)) lstOverview.Items.Add(telList); } } I sometimes see a little delay when entering a character, especially when i go from 4 records to 200 records (so when i had a filter and 4 records matched, and i backspace and the whole list appears again). My list is a list of usercontrols, cause i found it takes less time to load the usercontrols from a list, then to have to initialize a new usercontrol each time. Can i do something about the code, or is it just adding the usercontrol the listbox that causes the small delay (small delay = <1 sec)? Thanks in advance.

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• Existing LINQ extension method similar to Parallel.For?

  - by Joel Martinez

  The linq extension methods for ienumerable are very handy ... but not that useful if all you want to do is apply some computation to each item in the enumeration without returning anything. So I was wondering if perhaps I was just missing the right method, or if it truly doesn't exist as I'd rather use a built-in version if it's available ... but I haven't found one :-) I could have sworn there was a .ForEach method somewhere, but I have yet to find it. In the meantime, I did write my own version in case it's useful for anyone else: using System.Collections; using System.Collections.Generic; public delegate void Function<T>(T item); public delegate void Function(object item); public static class EnumerableExtensions { public static void For(this IEnumerable enumerable, Function func) { foreach (object item in enumerable) { func(item); } } public static void For<T>(this IEnumerable<T> enumerable, Function<T> func) { foreach (T item in enumerable) { func(item); } } } usage is: myEnumerable.For<MyClass>(delegate(MyClass item) { item.Count++; });

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• Parsing a list of dictionaries passed as a POST parameter

  - by andyashton

  I have a list of python dictionaries that look like this: sandwiches = [ {'bread':'wheat', 'topping':'tomatoes', 'meat':'bacon'}, {'bread':'white', 'topping':'peanut butter', 'meat':'bacon'}, {'bread':'sourdough', 'topping':'cheese', 'meat':'bacon'} ] I want to pass this as a POST parameter to another Django app. What does the client app need to do to iterate through the list? I want to do something like: for sandwich in request.POST['sandwiches']: print "%s on %s with %s is yummy!" % (sandwich['meat'], sandwich['bread'], sandwich['topping']) But I don't seem to have a list of dicts when my data arrives at my client app.

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• The fastest way to iterate through a collection of objects

  - by Trev

  Hello all, First to give you some background: I have some research code which performs a Monte Carlo simulation, essential what happens is I iterate through a collection of objects, compute a number of vectors from their surface then for each vector I iterate through the collection of objects again to see if the vector hits another object (similar to ray tracing). The pseudo code would look something like this for each object { for a number of vectors { do some computations for each object { check if vector intersects } } } As the number of objects can be quite large and the amount of rays is even larger I thought it would be wise to optimise how I iterate through the collection of objects. I created some test code which tests arrays, lists and vectors and for my first test cases found that vectors iterators were around twice as fast as arrays however when I implemented a vector in my code in was somewhat slower than the array I was using before. So I went back to the test code and increased the complexity of the object function each loop was calling (a dummy function equivalent to 'check if vector intersects') and I found that when the complexity of the function increases the execution time gap between arrays and vectors reduces until eventually the array was quicker. Does anyone know why this occurs? It seems strange that execution time inside the loop should effect the outer loop run time.

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• Optimal way to generate list of PHP object properties with delimiter character, implode()?

  - by Kris

  I am trying to find out if there is a more optimal way for creating a list of an object's sub object's properties. (Apologies for the crude wording, I am not really much of an OO expert) I have an object "event" that has a collection of "artists", each artist having an "artist_name". On my HTML output, I want a plain list of artist names delimited by a comma. PHP's implode() seems to be the best way to create a comma delimited list of values. I am currently iterating through the object and push values in a temporary array "artistlist" so I can use implode(). That is the shortest I could come up with. Is there a way to do this more elegant? $artistlist = array(); foreach ($event->artists as $artist) { $artistlist[] = $artist->artist_name; } echo implode(', ', $artistlist);

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