flat

Flatten nested lists to given depth.

Alternatives: flat, flatMap.

function flat(x, n, fm, ft)
// x:  nested lists
// n:  maximum depth [-1 ⇒ all]
// fm: map function (v, k, x)
// ft: test function for flatten (v, k, x) [is]

const xlists = require('extra-lists');

var x = [['ab', 'cde'], [
  [['a', 'b'], [1, 2]],
  [['c', 'de'], [
    3,
    [['d', 'e'], [
      3,
      [['e'], [
        5
      ]]
    ]]
  ]]
]];
xlists.flat(x).map(c => [...c]);
// → [ [ 'a', 'b', 'c', 'd', 'e' ], [ 1, 2, 3, 3, 5 ] ]

xlists.flat(x, 1).map(c => [...c]);
// → [ [ 'a', 'b', 'c', 'de' ], [ 1, 2, 3, [ [Array], [Array] ] ] ]

xlists.flat(x, 2).map(c => [...c]);
// → [ [ 'a', 'b', 'c', 'd', 'e' ], [ 1, 2, 3, 3, [ [Array], [Array] ] ] ]

References

• Array.prototype.flat: MDN web docs
• _.flatten: lodash
• _.flattenDeep: lodash
• _.flattenDepth: lodash
• Array.flatten: sugarjs