JAVASCRIPT

lodash find duplicate element index

const _ = require('lodash');
let arr = ["a", "a", "b", "c", "c", "a"];

let result = _.omitBy(
  _.reduce(arr, (a, v, i) => _.set(a, v, (a[v] || []).concat([i])), {} ),
  v => v.length <= 1
);

console.log(result);

lodash count duplicates in array

const data = ["apple", "banana", "apple", "orange", "grapes", "mango", "banana"];

const result = _.values(_.groupBy(data)).map(d => ({name: d[0], count: d.length}));

console.log(result);