Javascript Equivalent to C LINQ Select

Question

Following this question here       Using the checked binding in knockout with a list of checkboxes checks all the checkboxes   I ve created some checkboxes using knockout that allow selection from an array  working fiddle taken from above post      http   jsfiddle net NsCXJ    Is there a simple way of creating an array of just the fruit s ID s   I m more at home with C  where I would do something along the lines of selectedFruits select fruit  gt fruit id    Is there some method ready made function for doing something similar with javascript jquery   Or would the simplest option be to loop through the list and create a second array  I intend to post the array back to the server in JSON so am trying to minimize the data sent

User · Answer

I am answering the title of the question rather than the original question which was more specific.

With the new features of Javascript like iterators and generator functions and objects, something like LINQ for Javascript becomes possible. Note that linq.js, for example, uses a completely different approach, using regular expressions, probably to overcome the lack of support in the language at the time.

With that being said, I've written a LINQ library for Javascript and you can find it at https://github.com/Siderite/LInQer. Comments and discussion at https://siderite.dev/blog/linq-in-javascript-linqer.

From previous answers, only Manipula seems to be what one would expect from a LINQ port in Javascript.

User · Answer

You can also try linq js  In linq js your  selectedFruits select fruit  gt fruit id     will be   Enumerable From selectedFruits  Select function  fruit    return fruit id

User · Answer

The most similar C  Select analogue would be a map function  Just use   var ids   selectedFruits map fruit   gt  fruit id     to select all ids from selectedFruits array   It doesn t require any external dependencies  just pure JavaScript  You can find map documentation here  https   developer mozilla org en-US docs Web JavaScript Reference Global Objects Array map

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The ES6 way   let people     firstName  Alice  lastName  Cooper    firstName  Bob  age  Dylan     let names   Array from people  p   gt  p firstName   for  let name of names      console log name       also at  https   jsfiddle net 52dpucey

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Take a look at fluent  it supports almost everything LINQ does and based on iterables - so it works with maps  generator functions  arrays  everything iterable

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I know it is a late answer but it was useful to me  Just to complete  using the   grep function you can emulate the linq where     Linq   var maleNames   people  Where p   gt  p Sex     M    Select p   gt  p Name    Javascript      replace where  with   grep            select with   map var maleNames     grep people  function  p    return p Sex     M                   map function  p    return p Name

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Take a peek at underscore js which provides many linq like functions  In the example you give you would use the map function

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Yes  Array map   or   map   does the same thing     array map  var ids   this fruits map function v       return v Id         jQuery map  var ids2     map this fruits  function  v       return v Id       console log ids  ids2     http   jsfiddle net NsCXJ 1   Since array map isn t supported in older browsers  I suggest that you stick with the jQuery method   If you prefer the other one for some reason you could always add a polyfill for old browser support   You can always add custom methods to the array prototype as well   Array prototype select   function expr       var arr   this        do custom stuff     return arr map expr     or   map expr       var ids   this fruits select function v       return v Id          An extended version that uses the function constructor if you pass a string  Something to play around with perhaps   Array prototype select   function expr       var arr   this       switch typeof expr            case  function               return   map arr  expr               break           case  string                try                   var func   new Function expr split      0                                            return     expr                         return   map arr  func                 catch e                    return null                             break           default              throw new ReferenceError  expr not defined or not supported                break             console log fruits select  x Id       http   jsfiddle net aL85j   Update   Since this has become such a popular answer  I m adding similar my where      firstOrDefault    These could also be used with the string based function constructor approach  which is the fastest   but here is another approach using an object literal as filter   Array prototype where   function  filter         var collection   this       switch typeof filter              case  function                return   grep collection  filter             case  object               for var property in filter                  if  filter hasOwnProperty property                      continue     ignore inherited properties                collection     grep collection  function  item                      return item property      filter property                                               return collection slice 0      copy the array                                            in case of empty object filter           default               throw new TypeError  func must be either a                     function or an object of properties and values to filter by                Array prototype firstOrDefault   function func       return this where func  0     null       Usage   var persons      name   foo   age  1      name   bar   age  2         returns an array with one element  var result1   persons where   age  1  name   foo          returns the first matching item in the array  or null if no match var result2   persons firstOrDefault   age  1  name   foo         Here is a jsperf test to compare the function constructor vs object literal speed  If you decide to use the former  keep in mind to quote strings correctly   My personal preference is to use the object literal based solutions when filtering 1-2 properties  and pass a callback function for more complex filtering   I ll end this with 2 general tips when adding methods to native object prototypes    Check for occurrence of existing methods before overwriting e g    if  Array prototype where        Array prototype where       If you don t need to support IE8 and below  define the methods using Object defineProperty to make them non-enumerable  If someone used for  in on an array  which is wrong in the first place  they will iterate enumerable properties as well  Just a heads up

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Had to merge this nice answers  It revealed something like that  Extension   Array prototype where   function  filter                                     var collection   this                                   switch  typeof filter                                         case  function                                           return   grep collection  filter                                        case  object                                           for  var property in filter                                                if   filter hasOwnProperty property                                                   continue     ignore inherited properties                                              collection     grep collection  function  item                                                    return item property      filter property                                                                                                                                     return collection slice 0      copy the array                                          in case of empty object filter                                       default                                          throw new TypeError  func must be either a                                                 function or an object of properties and values to filter by                                                                      Usage    masterTableView get dataItems   where function  t    if  t findElement  quot  invoiceGridCheckbox quot   checked        invoiceIds push t getDataKeyValue  quot Id quot

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You can try manipula package  which implement all of C  LINQ methods and save its syntax  https   github com litichevskiydv manipula  https   www npmjs com package manipula  Your example selectedFruits select fruit  gt fruit id   will be implemented with manipula as  Manipula from selectedFruits  select fruit  gt fruit id

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Since you re using knockout  you should consider using the knockout utility function arrayMap   and it s other array utility functions   Here s a listing of array utility functions and their equivalent LINQ methods   arrayFilter   - gt  Where   arrayFirst   - gt  First   arrayForEach   - gt   no direct equivalent  arrayGetDistictValues   - gt  Distinct   arrayIndexOf   - gt  IndexOf   arrayMap   - gt  Select   arrayPushAll   - gt   no direct equivalent  arrayRemoveItem   - gt   no direct equivalent  compareArrays   - gt   no direct equivalent    So what you could do in your example is this   var mapped   ko utils arrayMap selectedFruits  function  fruit        return fruit id        If you want a LINQ like interface in javascript  you could use a library such as linq js which offers a nice interface to many of the LINQ methods   var mapped   Enumerable From selectedFruits       Select    id      1 of 3 different ways to specify a selector function      ToArray

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I have build a Linq library for TypeScript under TsLinq codeplex com that you can use for plain javascript too  That library is 2-3 times faster than Linq js and contains unit tests for all Linq methods  Maybe you could review that one

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Dinqyjs has a linq-like syntax and provides polyfills for functions like map and indexOf  and has been designed specifically for working with arrays in Javascript

[javascript] Javascript Equivalent to C# LINQ Select

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