Remap Array To Object

I have an array like this: var records = [{ 'field1': 'dogs', 'field2': 'poodle' }, { 'field1': 'dogs', 'field2': 'alsatian' }, { 'field1': 'dogs', 'field2': 'chowchow'

Solution 1:

It would be much simpler to group the pets by type first and then reformat the result into an array:

var group, pets = [], groups = {};
for (var i = 0; i < records.length; ++i) {
    group = groups[records[i].field1] || groups[records[i].field1] = [];
    group.push(records[i].field2);
}

for (var typeingroups) {
    if (!groups.hasOwnProperty(type)) continue; // just to be on the safe side
    pets.push({ type: type, breeds: groups[type] });
}

The .hasOwnProperty check is standard procedure to avoid unpleasant surprises from third party code.

Solution 2:

A possible solution in ECMA5.

var records = [{
        "field1": "dogs",
        "field2": "poodle"
    }, {
        "field1": "dogs",
        "field2": "alsatian"
    }, {
        "field1": "dogs",
        "field2": "chowchow"
    }, {
        "field1": "dogs",
        "field2": "schnauzer"
    }, {
        "field1": "cats",
        "field2": "siamese"
    }, {
        "field1": "cats",
        "field2": "persian"
    }, {
        "field1": "fish",
        "field2": "guppy"
    }, {
        "field1": "fish",
        "field2": "tiger barb"
    }],

    x = records.reduce(function (acc, record) {
        if (!acc[record.field1]) {
            acc[record.field1] = [];
        }

        if (acc[record.field1].indexOf(record.field2) === -1) {
            acc[record.field1].push(record.field2);
        }

        return acc;
    }, {}),

    y = Object.keys(x).map(function (key) {
        return {
            type: key,
            breeds: this[key]
        };
    }, x);

document.getElementById('out').textContent = JSON.stringify(y, null, 2);

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