Js array methods lost when iterating through an array of arrays?

Question

I have an array of arrays, and when I iterate through them with foreach, I try to call flatmap on the items, but js says flatmap is not a function

var arrayItems = [];
arrayItems.push(["a", "b", "c", "d", "e"]);
arrayItems.push(["c", "d", "e", "f"]);
arrayItems.push(["c", "e", "f", "g", "h"]);
arrayItems.push(["e", "f", "g", "h"]);

var variations = generate_variations(arrayItems);

function generate_variations(arrayItems) {

  var variations = [];
  //https://stackoverflow.com/questions/43241174/javascript-generating-all-combinations-of-elements-in-a-single-array-in-pairs/43241287

  arrayItems.forEach(([key, value]) =>
    variations.push(value.flatMap(
      (v, i) => value.slice(i + 1).map(w => [v, w])
    )));

  return variations;
}

console.log(variations);

Here is a simple flatmap that works fine (I tried to place this in a for loop) from Javascript - Generating all combinations of elements in a single array (in pairs)

var array = ["apple", "banana", "lemon", "mango"];

var result = array.flatMap(
  (v, i) => array.slice(i + 1).map(w => [v, w])
);

console.log(result);

`arrayItems.forEach(([key, value]) =>` this is not what `forEach` passes to the callback. — tkausl, Apr 17 '21 at 10:38
`key` is the first element of the nested array, and `value` is the second element. So they're both strings, `value` is not an array. — Barmar, Apr 17 '21 at 10:39
oh wow, never heard of that, trying it now :) https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/entries — giorgio79, Apr 17 '21 at 10:41
Why do you think you need it? You're not using `key` for anything. — Barmar, Apr 17 '21 at 10:42
True, I dont need it. I thought it is just good practice to have it in there. — giorgio79, Apr 17 '21 at 10:43

score 2 · Accepted Answer · answered Apr 17 '21 at 10:42

Change this line:

arrayItems.forEach(([key, value]) =>

To:

arrayItems.forEach((value) =>

var arrayItems = [];
arrayItems.push(["a", "b", "c", "d", "e"]);
arrayItems.push(["c", "d", "e", "f"]);
arrayItems.push(["c", "e", "f", "g", "h"]);
arrayItems.push(["e", "f", "g", "h"]);

var variations = generate_variations(arrayItems);


function generate_variations(arrayItems) {

  var variations = [];
  //https://stackoverflow.com/questions/43241174/javascript-generating-all-combinations-of-elements-in-a-single-array-in-pairs/43241287

  arrayItems.forEach((value) => 
    variations.push( value.flatMap(
      (v, i) => value.slice(i + 1).map(w => [v, w])
    )));
    
  return variations;
}

console.log(variations);

Wow that works! Interesting, leaving away key makes it work. — giorgio79, Apr 17 '21 at 10:44
In the syntax of `forEach()`, the value is the [first argument in the callback function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/forEach#syntax). — sbgib, Apr 17 '21 at 10:46

Js array methods lost when iterating through an array of arrays?

1 Answers1