using underscorejs to filter 2-dimensional array

Question

I have this array in javascript: you can see it here

 Array
(
    [2012-10-01] => Array
        (
            [1] => 1
            [2] => 0

...
            [148] => 0
            [149] => 0
            [150] => 1
        )

[2012-10-02] => Array
        (
            [1] => 0
            [2] => 1

...
            [148] => 0
            [149] => 1
            [150] => 0
        )

[2012-10-03] => Array
        (
            [1] => 1
            [2] => 0

...
            [148] => 0
            [149] => 0
            [150] => 1
        )
..............

to reduce it, I want to keep only items whose have ones and omit the items with zeros. like this

    Array
(
    [2012-10-01] => Array
        (
            [23] => 1
            [64] => 1
            [70] => 1
            [73] => 1
            [76] => 1
            [108] => 1
            [138] => 1
        )

I used underscorejs and this code:

 var new_o={};
    var v = _.each(original_array,function(day,key){
        var arr = {};
        _.map(day,function(item,k){
             if (item){
                 arr[k]=item;
             }
        }) ;

        new_o[key]= arr;
    } )    ;

it works, but I am pretty sure, I didn't get the best of underscore. can anybody suggest a smarter way?

what I was trying to say is that you could post the array using javascript syntax to make it easier for potential posters to test your code. — georg
– georg, Commented Oct 31, 2012 at 15:25
please look at the fiddle fiddle.jshell.net/LBa5A/1 (I edited the question above and added a link to the fiddle) — Aladdin Mhemed
– Aladdin Mhemed, Commented Oct 31, 2012 at 15:44

mu is too short · Accepted Answer · 2012-10-31 16:30:16Z

2

Don't use _.map if you don't use its return value, that's just a slightly more expensive version of _.each.

As far as simplifying things goes, you're a bit stuck because both Underscore and JavaScript really want to iterate over arrays and you have nested objects (BTW, { } is an object literal in JavaScript, [ ] is an array, they are quite different). Probably the best you can do with your current data structure is to use _.reduce to iterate over the sub-objects while carrying the new sub-object along; something like this:

var new_o = { };
_.each(original, function(day, key) {
    new_o[key] = _(day).reduce(function(memo, item, k) {
        if(item)
            memo[k] = item;
        return memo;
    }, { });
});

Demo: http://jsfiddle.net/ambiguous/FZRV3/

answered Oct 31, 2012 at 16:30

mu is too short

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2 Comments

Aladdin Mhemed Over a year ago

thank you. Would you please tell me, how would it be if it was arrays? I mean if the structures were arrays.

mu is too short Over a year ago

That would depend on what your array version of the data looked like but it would probably involve _.filter.

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