Find the longest array within an object (within another object) in javascript

Question

I have an object of objects. Within those objects are arrays, that have more objects. Below is the structure.

I want to find out what the longest array of objects is within the parent object. So in my example below:

For ObjectOne - the longest array is B.

For ObjectTwo, the longest array is C.

mainobj = {
    ObjectOne: { 
        A: [ 
             { x: 'd', y: 'e'},
             { x: 'd', y: 2} 
           ],
        B: [ 
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'} 
           ],
        C: [ 
             { x: 'd', y: 'e'} 
           ]
    },
    ObjectTwo:{ 
        A: [
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'}
           ],
        B: [
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'}
           ],
        C: [
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'},
             { x: 'd', y: 'e'}
           ]
    }
}

I can do this:

var size = Object.values(mainobj).length

but I don't know how to get deeper than that. For instance, this doesn't work:

var size = Object.values(mainobj)[0].length

This question is pretty similar, but I can't figure out how to apply it. I appreciate the help!

Answer 1

You can convert your objet to keep only arrays which have the max length:

var    mainObj =   {
                    1:{ 
                            A: [
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 2}
                                    ],
                            B: [
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'}
                                    ],
                            C: [
                                        { x: 'd', y: 'e'}
                                    ]
                        },
                    2:{ 
                            A: [
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'}
                                    ],
                            B: [
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'}
                                    ],
                            C: [
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'},
                                        { x: 'd', y: 'e'}
                                    ]
                        }
                };

var res = {};

Object.keys(mainObj).forEach(key => {
    var maxLength = 0, nameOfmaxLenghtArray, maxLenghtArray;
    Object.keys(mainObj[key]).forEach(arrayName => {
        if (mainObj[key][arrayName].length > maxLength) {
            maxLengthArrayName = arrayName;
            maxLenghtArray = mainObj[key][arrayName];
            maxLength = mainObj[key][arrayName].length;
        }
    });
    res[key] = { [maxLengthArrayName ]: maxLenghtArray};
});

console.log('res: ', res);

// You can then access the max length array for each sub-object of mainobj:

var subObject = '1';
var maxLengthArrayName = Object.keys(res[subObject])[0];
var maxLengthArray = Object.values(res[subObject])[0];

console.log(`max length array name for sub-object ${subObject}: `, maxLengthArrayName);
console.log(`max length array for sub-object ${subObject}: `, maxLengthArray );

Answer 2

You could return an object for each outer key and get an array with the largest inner array's keys.

var object = { objectOne: { A: [{ x: 'd', y: 'e' }, { x: 'd', y: 2 }], B: [{ x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }], C: [{ x: 'd', y: 'e' }] }, objectTwo: { A: [{ x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }], B: [{ x: 'd', y: 'e' }, { x: 'd', y: 'e' }], C: [{ x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }, { x: 'd', y: 'e' }] } },
    result = Object.keys(object).map(function (k) {
        var o = object[k];
        return {
            key: k,
            items: Object.keys(o).reduce(function (r, l, i) {
                if (!i || o[r[0]].length < o[l].length) {
                    return [l];
                }
                if (o[r[0]].length === o[l].length) {
                    r.push(l);
                }
                return r;
            }, [])
        };
    });

console.log(result);

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