This question as a JS-only answer here. But simply because I'd like to become more proficient with Lodash, I'm looking for the Lodash solution.
Let's say I have an array that looks like:
[[a, b, c], [d, e, f], [h, i, j]]
I'd like to get the first element of each array as its own array:
[a, d, h]
What is the most efficient way to do this with Lodash? Thanks.
You could use _.map with _.head for the first element.
var data = [['a', 'b', 'c'], ['d', 'e', 'f'], ['h', 'i', 'j']],
result = _.map(data, _.head);
console.log(result);<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>Or just the key.
var data = [['a', 'b', 'c'], ['d', 'e', 'f'], ['h', 'i', 'j']],
result = _.map(data, 0);
console.log(result);<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>
If you want to use lodash:
const _ = require('lodash')
const arr1 = [[a, b, c], [d, e, f], [h, i, j]]
arr2 = _.map(arr1, e => e[0])
With lodash you can do this with _.first, _.head (_.first is just an alias of _.head) and direct path while mapping through the array:
const data = [['a', 'b', 'c'], ['d', 'e', 'f'], ['h', 'i', 'j']]
console.log(_.map(data, _.first))
console.log(_.map(data, _.head))
console.log(_.map(data, 0)) // direct path<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>If you however have to use lodash just for this then simply use either ES6 or ES5:
const data = [['a', 'b', 'c'], ['d', 'e', 'f'], ['h', 'i', 'j']]
console.log(data.map(x => x[0]))
console.log(data.map(function(x){ return x[0] }))The performance and actual code is the same practically.
https://lodash.com/docs/#filter
Use the docs, look for some each function.
let arr = [[a, b, c], [d, e, f], [h, i, j]]
let newArray = _.filter(arr, function(subArray){
return subArray[0] // first element of each subArray
})
console.log(newArray)
This should do it, but I don't understand why you wanna use lodash when pretty much the same filter function exists in vanilla javascript.
You can also use the _.matchesProperty iteratee shorthand, which many lodash methods support.
const data = [['a', 'b', 'c'], ['d', 'e', 'f'], ['h', 'i', 'j']];
const result = _.map(data, '[0]');
console.log(result);<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>
let result = arr.map(a => a[0])let result = _.map(arr, a => a[0]);