Question

I have the following array format:

var myArr = [
{
    "a": "1",
    "b": "2",
    "c": "3",
    "d" {
        "0" : "1",
        "1" : "2"
    },
    "blah" : "me"
},
{
    "a": "5",
    "b": "3",
    "c": "1",
    "d" {
        "0" : "6",
        "1" : "3"
    },
    "blah" : "me"
},
{
    "a": "5",
    "b": "3",
    "c": "1",
    "d" {
        "0" : "6",
        "1" : "3"
    },
    "blah" : "you"
}
]

I am wondering how I could map a new array such that the values under “blah” are together like

var myArr = [{
    "me" : [
    {
        "a": "1",
        "b": "2",
        "c": "3",
        "d": {
            "0" : "1",
            "1" : "2"
            }
    },
    {
        "a": "5",
        "b": "3",
        "c": "1",
        "d": {
            "0" : "6",
            "1" : "3"
            }
    }
    ],
    "you" : [
    {
        "a": "5",
        "b": "3",
        "c": "1",
        "d": {
            "0" : "6",
            "1" : "3"
            }
    }
    ]
}]

Answer 1

That’s very possible, try this:

var output = {};
myArr.forEach(function(elem){     // Loop trough the elements in `myArr`
    if(!output[elem.blah]){       // If the output object doesn't have a property named by elem.blah, yet
        output[elem.blah] = [];   // Create a empty array
    }
    output[elem.blah].push(elem); // Push the current element to that array
    delete elem.blah;             // And delete the mention of `blah` from it (optional)
});

Instead of forEach, you can also use a normal for loop, for more compatibility:

var output = {};
for(var i = 0; i < myArr.length; i++){ // Loop trough the elements in `myArr`
    var elem = myArr[i];
    if(!output[elem.blah]){            // If the output object doesn't have a property named by elem.blah, yet
        output[elem.blah] = [];        // Create a empty array
    }
    output[elem.blah].push(elem);      // Push the current element to that array
    delete elem.blah;                  // And delete the mention of `blah` from it (optional)
});

With underscore.js, you can just do this:

_.groupBy(myArr, 'blah');

the only difference is that this won’t remove the blah property from the source objects.