Javascript Array Map 2D array

Question

I'm trying to aggregate the array (arr) below so that I get an output such as:

Desired Output: [['2011-04-11','Open',6],['2011-04-11','Closed',4]]

but I'm getting: Output: [2011-04-11,Open: 6, 2011-04-11,Closed: 4]

How can I take the javascript array map and convert to desired out.

Source code excerpt:

var arr = [
    ['2011-04-11', 'Open'],
    ['2011-04-11', 'Closed'],
    ['2011-04-11', 'Closed'],
    ['2011-04-11', 'Open'],
    ['2011-04-11', 'Open'],
    ['2011-04-11', 'Open'],
    ['2011-04-11', 'Closed'],
    ['2011-04-11', 'Closed'],
    ['2011-04-11', 'Open'],
    ['2011-04-11', 'Open']
];

var hist = [];
arr.map(function(a) {
   if (a in hist)
      hist[a]++;
   else
      hist[a] = 1;
});

You don't need an extra array when you use map, just return something. Also you want to use indexOf not in when working with arrays. Otherwise use an object if your keys are not numeric. — elclanrs
– elclanrs, Commented Mar 11, 2014 at 3:12

Ja͢ck · Accepted Answer · 2014-03-11 03:25:16Z

5

You can use [].reduce() instead:

var result = function() {
    var hist = {};

    return arr.reduce(function(previous, current) {
        if (current in hist) {
            previous[hist[current]][2]++;
        } else {
            previous[hist[current] = previous.length] = current.concat(1);
        }
        return previous;
    }, []);
}();

During the reduce operation, it uses hist to keep track of where each item can be found in the new array that's being built.

If the item already exists, it will increase its frequency element (third element). If the item does not yet exist, it will set its frequency to 1 and update hist to the position of the new item.

Demo

edited Mar 11, 2014 at 3:25

answered Mar 11, 2014 at 3:18

Ja͢ck

174k39 gold badges269 silver badges316 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

thefourtheye Over a year ago

+1 Clever. I came up with

console.log(arr.reduce(function(tillNow, currentItem) {     tillNow[currentItem] = (tillNow[currentItem] || 0) + 1;     return tillNow; }, {}));

and got stuck :'(

Collectives™ on Stack Overflow

Javascript Array Map 2D array

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related