Extract array of objects based on their content

Question

In JavaScript I have a JSON array like this:

var r = [{"name":"a","bool":false},{"name":"b","bool":false},
         {"name":"c","bool":false},{"name":"a","bool":false},
         {"name":"b","bool":false},{"name":"c","bool":true},
         {"name":"a","bool":true}];

I want to build another array containing all the objects where name=="a" and bool==false. I solved this by looping, but I wanted to know if there is another way to do it.

How can I do?

[edit] My loop was:

var rLen = r.length;
var newArray = [];

for(var i=0;i<rLen;i++) {
    if(r[i].name=="a"&&r[i].bool==false) {
        newArray.push(r[i]);
    }
}

Looping is the way to do it, but could you please show your current loop code? This question is possibly better suited on codereview.stackexchange.com. — James Donnelly
– James Donnelly, Commented Oct 9, 2014 at 11:05
@JamesDonnelly Why should he post it on codereview? He doesn't have a solution to review :) — Johan
– Johan, Commented Oct 9, 2014 at 11:06
@Johan the question states: "I solved this by looping, but I wanted to know if there is another way to do it.". OP is effectively asking if there's a better way to achieve the code which has already been written - which isn't displayed in the question. — James Donnelly
– James Donnelly, Commented Oct 9, 2014 at 11:08

Johan · Accepted Answer · 2014-10-09 11:11:02Z

In the end it will always be solved by loops internally, e.g.

var r = [{"name":"a","bool":false},{"name":"b","bool":false},
         {"name":"c","bool":false},{"name":"a","bool":false},
         {"name":"b","bool":false},{"name":"c","bool":true},
         {"name":"a","bool":true}];

var result = r.filter(function(item){
    return item.name === 'a' && !item.bool;
});

If you look at the polyfill, you'll notice the loop:

if (!Array.prototype.filter) {
  Array.prototype.filter = function(fun/*, thisArg*/) {
    'use strict';

    if (this === void 0 || this === null) {
      throw new TypeError();
    }

    var t = Object(this);
    var len = t.length >>> 0;
    if (typeof fun !== 'function') {
      throw new TypeError();
    }

    var res = [];
    var thisArg = arguments.length >= 2 ? arguments[1] : void 0;
    for (var i = 0; i < len; i++) { // <-- 
      if (i in t) {
        var val = t[i];

        // NOTE: Technically this should Object.defineProperty at
        //       the next index, as push can be affected by
        //       properties on Object.prototype and Array.prototype.
        //       But that method's new, and collisions should be
        //       rare, so use the more-compatible alternative.
        if (fun.call(thisArg, val, i, t)) {
          res.push(val);
        }
      }
    }

    return res;
  };
}

Since you're interested in performance, here is a jsperf comparing the two: http://jsperf.com/aarontgrogg-array-filter-vs-for-loop

TSV · Accepted Answer · 2014-10-09 11:05:46Z

1

may be

var r1 = r.filter(function(item){ return item.name === "a" && !item.bool; });

answered Oct 9, 2014 at 11:05

TSV

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