Suppose, we have an array string that contains some duplicate entries like this −
const arr = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California'];
We are required to write a JavaScript function that takes in one such array. Our function should then construct an array of objects that contains an object for each unique entry and a property "count" that contains its count in the original array.
Therefore, the final output for the above array should look something like this −
const output = [ {'name':'California', 'count':2}, {'name':'Texas', 'count':3}, {'name':'New York', 'count':1}, {'name':'Missouri', 'count':1}, {'name':'New Mexico', 'count':1}, ];
Example
The code for this will be −
const arr = ['California','Texas','Texas','Texas','New York','Missouri','New Mexico','California']; const findOccurrences = (arr = []) => { const res = []; arr.forEach(el => { const index = res.findIndex(obj => { return obj['name'] === el; }); if(index === -1){ res.push({ "name": el, "count": 1 }) } else{ res[index]["count"]++; }; }); return res; }; console.log(findOccurrences(arr));
Output
And the output in the console will be −
[ { name: 'California', count: 2 }, { name: 'Texas', count: 3 }, { name: 'New York', count: 1 }, { name: 'Missouri', count: 1 }, { name: 'New Mexico', count: 1 } ]