Converting nested array elements to array of strings

Question

Given a simple array of nested arrays like this:

[
  ['a','b',],
  ['c','d'],
  ['e']
]

I'm looking to concatenate the values from each element and create an array like this:

['.a.c.e','.a.d.e','.b.c.e','.b.d.e']

This is just a simple example but in reality there could be more than 3 nested arrays and any number of elements within them.

Seems like it should be relatively simple, but I just can't wrap my brain around it, can anyone help?

It's not clear how your input array relates to your expected output. Could you expand on what you are trying to do — Brett Gregson, Oct 24 '19 at 08:37
I'm basically trying to construct a jquery class selector where the output has every combination of input values. So you can see in my question, there are 2 x 2 x 1 possible combinations, so 4 results. Obviously if there were more elements in each array or more arrays, there would be more possible combinations. I basically need an array with all the possible combinations — the_lar, Oct 24 '19 at 08:51

marzelin · Accepted Answer · 2019-10-24T09:52:40.690

Since the array length is unknown, the best way is to use recursion:

function conc(input) {
  const output = [];
  function _conc(input, partial) {
    if (input.length === 0) {
      return output.push(partial);
    }
    const [first, ...rest] = input;
    first.forEach(itm => {
      _conc(rest, partial + "." + itm)
    });
  }
  _conc(input, "");
  return output;
}

const input = [
  ['a','b',],
  ['c','d'],
  ['e']
]

console.log(conc(input))

or with flatMap:

function conc(input) {
  const [first, ...rest] = input;
  return rest.length === 0
    ? first.map(itm => "." + itm)
    : first.flatMap(itm => conc(rest).map(_itm => "." + itm + _itm));
}

const input = [
  ['a','b',],
  ['c','d'],
  ['e']
]

console.log(conc(input))

or with reduce:

const input = [
  ['a','b',],
  ['c','d'],
  ['e']
]

console.log(
  input.reduce((acc, a) => acc.flatMap(i1 => a.map(i2 => i1 + "." + i2)), [""])
)

Converting nested array elements to array of strings

1 Answers1