Get the total count / length of arrays within objects ES6

Question

I'm trying to get the total length count of each array within their respective objects...

campus : {
    "mchale": {
        "classes":["ESJ030", "SCI339"], // get the length
        "faculty":["Hardy", "Vikrum"]   // get the length
     },
    "lawerence":{
        "classes":["ENG001"],  // get the length
        "faculty":["Speedman", "Lee", "Lazenhower"] // get the length
     }
}

This is what I have:

const arrCount = campus.mchale.classes.length + campus.mchale.faculty.length + campus.lawerence.classes.length ...

Is there a better/prettier way to go about this to retrieve the total count of each array present in the objects?

ssube · Accepted Answer · 2016-05-20 14:51:50Z

3

You can use Object.keys with map and reduce to collect the arrays, get their length, then sum those values:

const data = {
    "mchale": {
        "classes":["ESJ030", "SCI339"], // get the length
        "faculty":["Hardy", "Vikrum"]   // get the length
     },
    "lawerence":{
        "classes":["ENG001"],  // get the length
        "faculty":["Speedman", "Lee", "Lazenhower"] // get the length
     }
};

const count = Object.keys(data).map(campusName => {
  const campus = data[campusName];
  return Object.keys(campus).map(key => campus[key].length).reduce((p, c) => p + c, 0);
}).reduce((p, c) => p + c, 0);
console.log(count);

answered May 20, 2016 at 14:51

ssube

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2 Comments

Modelesq Over a year ago

mapping causes a warning thrown in console stating that i need unique ids for each mapped item. this doesn't necessarily need ids. But your solution works nontheless :)

ssube Over a year ago

What warning are you seeing? Array.prototype.map shouldn't be able to throw a warning and doesn't require unique IDs, or IDs of any kind.

Tushar · Accepted Answer · 2016-05-20 14:50:34Z

2

You can use Array#reduce with Object.keys() as follow.

Object.keys(campus).reduce((a, b) => campus[b].classes.length +
    campus[b].faculty.length + a, 0);

var campus = {
    "mchale": {
        "classes": ["ESJ030", "SCI339"], // get the length
        "faculty": ["Hardy", "Vikrum"] // get the length
    },
    "lawerence": {
        "classes": ["ENG001"], // get the length
        "faculty": ["Speedman", "Lee", "Lazenhower"] // get the length
    }
};

var length = Object.keys(campus).reduce((a, b) => campus[b].classes.length + campus[b].faculty.length + a, 0);
console.log(length);

answered May 20, 2016 at 14:50

Tushar

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Comments

madox2 · Accepted Answer · 2016-05-20 14:53:12Z

2

You can recursively traverse object key's and sum all lengths of array objects:

var campus = {
    "mchale": {
        "classes":["ESJ030", "SCI339"],
        "faculty":["Hardy", "Vikrum"]
     },
    "lawerence":{
        "classes":["ENG001"],
        "faculty":["Speedman", "Lee", "Lazenhower"]
     }
};

function totalArrayLength(obj) {
    return Object.keys(obj).reduce((total, key) => {
        if (Array.isArray(obj[key])) {
            total += obj[key].length;
        } else if (typeof obj[key] === 'object') {
            total += totalArrayLength(obj[key]);
        }
        return total;
    }, 0);
}

console.log(totalArrayLength(campus));

answered May 20, 2016 at 14:53

madox2

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