Javascript Array Filtering - http://www.paulfree.com/28/javascript-array-filtering/

where.js

Array.prototype.where =
   function(f)
   {
      var fn = f ;
      // if type of parameter is string         
      if ( typeof f == "string" )
         // try to make it into a function
         if ( ( fn = lambda( fn ) ) == null )
            // if fail, throw exception
            throw "Syntax error in lambda string: " + f ;
      // initialize result array
      var res = [] ;
      var l = this.length;
      // set up parameters for filter function call
      var p = [ 0, 0, res ] ;
      // append any pass-through parameters to parameter array               
      for (var i = 1; i < arguments.length; i++) p.push( arguments[i] );
      // for each array element, pass to filter function
      for (var i = 0; i < l ; i++)
      {
         // skip missing elements
         if ( typeof this[ i ] == "undefined" ) continue ;
         // param1 = array element             
         p[ 0 ] = this[ i ] ;
         // param2 = current indeex
         p[ 1 ] = i ;
         // call filter function. if return true, copy element to results            
         if ( !! fn.apply(this, p)  ) res.push(this[i]);
      }
      // return filtered result
      return res ;
   }
   
var a = [1,2,3,4,5,6,7,8,9,10];
    // return everything
    a.where( "( ) => true" ) ;
        --> [1,2,3,4,5,6,7,8,9,10]
    // return even numbers
    a.where( "( n, i ) => n % 2 == 0" ) ;
        --> [2,4,6,8,10]
    // using product table data from SQL Server's northwind database...    
    var products = [
          {key: 1, prod: "Chai", cat: "Beverages", units: 39, reorderlevel: 10},
          {key: 2, prod: "Chang", cat: "Beverages", units: 17, reorderlevel: 25},
          {key: 3, prod: "Aniseed Syrup", cat: "Condiments", units: 13, reorderlevel: 25},
          //....        
          {key: 75, prod: "Rhönbräu Klosterbier", cat: "Beverages", units: 125, reorderlevel: 25},
          {key: 76, prod: "Lakkalikööri", cat: "Beverages", units: 57, reorderlevel: 20},
          {key: 77, prod: "Original Frankfurter grüne Soße", cat: "Condiments", units: 32, reorderlevel: 15} ] ;
    // query beverages that need reordering using extra parameter
    products.where( "( el, i, res, param ) => el.units <= el.reorderlevel && el.cat == param" , "Beverages");
        --> {key: 2, prod: "Chang", cat: "Beverages", units: 17, reorderlevel: 25}
            {key: 43, prod: "Ipoh Coffee", cat: "Beverages", units: 17, reorderlevel: 25}
            {key: 70, prod: "Outback Lager", cat: "Beverages", units: 15, reorderlevel: 30}
    // query first 6 products whose category begins with 'con' using extra param and regular expression
    products.where( "( el, i, res, param ) => res.length <= 6 && param.test( el.cat )", new RegExp( "^con", "i") );
        --> {key: 3, prod: "Aniseed Syrup", cat: "Condiments", units: 13, reorderlevel: 25}
            {key: 4, prod: "Chef Anton's Cajun Seasoning", cat: "Condiments", units: 53, reorderlevel: 0}
            {key: 5, prod: "Chef Anton's Gumbo Mix", cat: "Condiments", units: 0, reorderlevel: 0}
            {key: 6, prod: "Grandma's Boysenberry Spread", cat: "Condiments", units: 120, reorderlevel: 25}
            {key: 8, prod: "Northwoods Cranberry Sauce", cat: "Condiments", units: 6, reorderlevel: 0}
            {key: 15, prod: "Genen Shouyu", cat: "Condiments", units: 39, reorderlevel: 5}
            {key: 16, prod: "Pavlova", cat: "Confections", units: 29, reorderlevel: 10}
    // using customer table data from SQL Server's northwind database...    
    var customers = [
        {name:"Maria Anders",city:"Berlin",zip:"12209",country:"Germany"},
        {name:"Ana Trujillo",city:"México D.F.",zip:"05021",country:"Mexico"},
        {name:"Antonio Moreno",city:"México D.F.",zip:"05023",country:"Mexico"},
        //...
        {name:"Karl Jablonski",city:"Seattle",zip:"98128",country:"USA"},
        {name:"Matti Karttunen",city:"Helsinki",zip:"21240",country:"Finland"},
        {name:"Zbyszek Piestrzeniewicz",city:"Warszawa",zip:"01-012",country:"Poland"}];
    // query customers in the USA
    customers.where( "( el, i, res, param ) => el.country == param", "USA" );
        --> {name:"Howard Snyder",city:"Eugene",zip:"97403",country:"USA"}
            {name:"Yoshi Latimer",city:"Elgin",zip:"97827",country:"USA"},
            {name:"John Steel",city:"Walla Walla",zip:"99362",country:"USA"}
            {name:"Jaime Yorres",city:"San Francisco",zip:"94117",country:"USA"}
            {name:"Fran Wilson",city:"Portland",zip:"97219",country:"USA"}
            {name:"Rene Phillips",city:"Anchorage",zip:"99508",country:"USA"}
            {name:"Paula Wilson",city:"Albuquerque",zip:"87110",country:"USA"}
            {name:"Jose Pavarotti",city:"Boise",zip:"83720",country:"USA"}
            {name:"Art Braunschweiger",city:"Lander",zip:"82520",country:"USA"}
            {name:"Liz Nixon",city:"Portland",zip:"97201",country:"USA"}
            {name:"Liu Wong",city:"Butte",zip:"59801",country:"USA"}
            {name:"Helvetius Nagy",city:"Kirkland",zip:"98034",country:"USA"}
            {name:"Karl Jablonski",city:"Seattle",zip:"98128",country:"USA"}