JavaScript select

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Posted on Friday December 2011

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Ooo I thought I was being clever. I was looking for an easy way to get the maximum value out of an array of numbers. John Resig had an answer, making clever use of the apply feature of javascript.

And that sparked me to thinkings: "If I can apply a function to every value in an eumerable... can I write a kind of LINQy select?"

And the answer is yes, yes you can:

  var select = function (property, array) {
       var result = { p: property, output: [] };
       __select.apply(result, array);
       return result.output;
   };

   var __select = function () {
       for (var i = 0; i < arguments.length; i++) {
           if (arguments[i][this.p]) {
               this.output.push(arguments[i][this.p]);
           }
       }
   };

And I was very chuffed and turned round to my co-worker David to show him.

"Uh-huh... so why don't you just call the select thingy function?"

Oh. Yeah. No need to complicate things. Damn. Not so chuffed anymore. Still this is a handy little function. The poor mans LINQ select, allowing you to "project" a property out of an array of objects.

   var select = function (property, array) {
       var result [];

       for (var i = 1; i < arguments.length; i++) {
           if (arguments[i][arguments[0]]) {
               result.push(arguments[i][arguments[0]]);
           }
       }

       return result;
   };

And to solve my original problem of finding the max value:

    var orders = [
        { orderNo: 1, orderValue:  123 },
        { orderNo: 1, orderValue:  321 },
        { orderNo: 1, orderValue:  456 }
     ];

    var orderValues = select(‘orderValue’, orders);
    // returns [123, 321, 456]
    Math.max.apply(Math, orderValues);

There are of course plenty of "real" LINQ for JavaScript and variations about. Cheers.