lodash mapby code example

Example 1: diff two arrays lodash

_.difference([2, 1], [2, 3]);
// => [1]

Example 2: 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);