Stuck on creating a function that will return objects

Question

Hi I was wondering if I can get some help here I am stuck. I am trying to create a histogram function that takes an array like ['a', 'a', 'b', 'c', 'b', 'a'] and returns {a:3, b:2, c:1} using the reduce function to build the histogram function. But I am stuck on what the callback function should be.

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Thank you for any responses.

Answer 1

Try to iterate over the array and fill/increment the object's value accordingly,

var x = ['a', 'a', 'b', 'c', 'b', 'a'];
var y = {};

x.forEach(function(itm){
 y[itm] = ++y[itm] || 1;
});

Answer 2

You can reduce your array like this:

['a', 'a', 'b', 'c', 'b', 'a'].reduce(function(obj, value) {
    obj[value] = obj[value] || 0;
    obj[value]++;
    return obj; 
}, {});

If your environment supports Object.assign() and ES6 you can also do this:

['a', 'a', 'b', 'c', 'b', 'a']
    .reduce((a, b) => Object.assign(a, {[b]: a[b] ? ++a[b] : 1}), {});