Javascript - How to concatenate string values from two arrays of different sizes?

Question

I have two arrays, for example:

Array1:

arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"]

Array2:

arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

I want to generate a new array from two above concatenating the individual items into new items recursively for each one in array1, to get a final array like this:

final = ['Precon-EJID', 'Contra-EJID', 'Postco-EJID', 'Cancel-EJID', 'Consul-EJID', 'Precon-EMBA', 'Contra-EMBA', 'Postco-EMBA', 'Cancel-EMBA', 'Consul-EMBA', 'Precon-EMPR', 'Contra-EMPR', 'Postco-EMPR', 'Cancel-EMPR', 'Consul-EMPR'...etc]

Thank you in advance

Possible duplicate of [Cartesian product of multiple arrays in JavaScript](https://stackoverflow.com/questions/12303989/cartesian-product-of-multiple-arrays-in-javascript) — pwolaq, Jan 23 '18 at 22:21
What have you tried? This can be done with a number of different loop approaches — charlietfl, Jan 23 '18 at 22:21
The multiple answers posted to this Question prove that the "downvote" and "close" vote standards and rationales, if any, are fully arbitrary and capricious. Which is ok. Just be aware that it is duly noted if any of the users whom answered this Question find the audacity to post a comment questioning this users' answering any question here at SO whatsoever. None of the users whom posted answers to this question should vote to close another question under the premise of "off-topic because -> ("why isn't this code working?")" else that vote is fraudulent even if only you know that fact — guest271314, Jan 23 '18 at 22:45

score 4 · Accepted Answer · answered Jan 23 '18 at 22:22

You can do this with 2 simple for of loops:

var arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"];

var arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

var finalArr = [];

for ( var item2 of arr2 ) {
  for ( var item1 of arr1 ) {
    finalArr.push(`${item1}-${item2}`);
  }
}

console.log(finalArr);

Ori Drori · Answer 2 · 2018-01-23T22:24:15.753

2

You can use nested Array#map calls, and flatten the results using Array#concat:

const arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"]

const arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

const result = [].concat(...arr2.map((s1) => arr1.map((s2) => `${s2}-${s1}`)))

console.log(result)

edited Jan 23 '18 at 22:24

answered Jan 23 '18 at 22:21

Ori Drori

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Solid answer. It's a little messy having to use the new spread syntax (`...`), but works and doesn't require a third "building array". – Blue Jan 24 '18 at 06:03

CRice · Answer 3 · 2018-01-23T22:31:12.897

0

Here's a one liner to do this:

arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"]
arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

const result = [].concat(...arr1.map(prefix => arr2.map(suffix => prefix+suffix)));
console.log(result)

// EDIT: if order matters, reverse the use of arr1 and arr2:

const orderedResult = [].concat(...arr2.map(suffix => arr1.map(prefix => prefix+suffix)));
console.log(orderedResult)

edited Jan 23 '18 at 22:31

answered Jan 23 '18 at 22:23

CRice

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why `[].concat`? – pwolaq Jan 23 '18 at 22:24
your output does not match desired output :p – Jaromanda X Jan 23 '18 at 22:24
Flattens the array so that all items are at the same level. Without it, the result would be a 2-dimensional array: `[["PreconEJID", ...], ["ContraEJID", ...], ...]` – CRice Jan 23 '18 at 22:25
@JaromandaX I though it did? In what way? OP's final array is not nested. Or do you mean the order is incorrect? – CRice Jan 23 '18 at 22:26
@CRice OP does not specify any particular ordering of the result – guest271314 Jan 23 '18 at 22:27
yep, `const result = [].concat(...arr2.map(suffix => arr1.map(prefix => prefix+suffix)));` – Jaromanda X Jan 23 '18 at 22:27
@guest271314 - *to get a final array like this* ... see the **order** in the partial output? it's obvious the OP wants tht order – Jaromanda X Jan 23 '18 at 22:28
Agree with @guest271314, I didn't think the order matters. But as @JaromandaX points out, reversing the use of `arr1` and `arr2` will solve that issue. EDIT: I've edited the answer to include the fixed ordering, just in case. – CRice Jan 23 '18 at 22:29
@JaromandaX That is a plausible interpretation of the Question. – guest271314 Jan 23 '18 at 22:29
The output order matters, I forget to mention that in the question, so this approach gets the correct result but in first array order. – Mark Hkr Jan 23 '18 at 22:34
This is pretty much @OriDrori's answer – Blue Jan 24 '18 at 13:25

Aluan Haddad · Answer 4 · 2018-01-23T22:40:02.920

0

const prefixes = [
  "Precon",
  "Contra",
  "Postco",
  "Cancel",
  "Consul"
];

const suffixes = [
  "EJID", "EMBA", "EMPR",
  "GOBI", "PART", "PPOL",
  "SACI", "SOFL", "SOFM",
  "0000", "", "0002",
  "0003", "0004", "0005",
  "0006", "0007", "0008",
  "0009", "0010", "0011",
  "0012", "0013", "0014",
  "0015", "0016", "011",
  "0110", "9999"
];

const results = suffixes
  .map(suffix => prefixes.map(prefix => prefix + '-' + suffix))
  .reduce((xs, ys) => [...xs, ...ys]);

console.log(results);

edited Jan 23 '18 at 22:40

answered Jan 23 '18 at 22:33

Aluan Haddad

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There should be dashes between the prefix/suffixes – Blue Jan 23 '18 at 22:39
@FrankerZ If we are positing what "should be". There should first be a modicum of effort put forth by OP to resolve their own inquiry, which is wholly absent from the Question. – guest271314 Jan 23 '18 at 22:40

score 0 · Answer 5 · answered Jan 23 '18 at 22:42

Another option is to use reduce...

let arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"]

let arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

let arr3 = arr2.reduce((arr, val) => {
    let f = []
    arr1.forEach(itm => val && f.push(itm + '-' + val))
    return arr.concat(f)
}, [])

console.log(arr3)

score 0 · Answer 6 · answered Jan 23 '18 at 22:58

Here's a recursive one. Just like the OP asked. Took me a while. :P

arr1 = ["Precon", "Contra", "Postco", "Cancel", "Consul"]

arr2 = ["EJID", "EMBA", "EMPR", "GOBI", "PART", "PPOL", "SACI", "SOFL", "SOFM", "0000", "", "0002", "0003", "0004", "0005", "0006", "0007", "0008", "0009", "0010", "0011", "0012", "0013", "0014", "0015", "0016", "011", "0110", "9999"]

var arr = [];

console.log(concat(arr1, arr2, 0, 0, 0));

function concat(arr1, arr2, arrIndex, index1, index2) {
  //console.log(arr1.length);
  if (index2 === (arr2.length)) {
    return;
  } else {
    arr[arrIndex] = arr1[index1] + '-' + arr2[index2];
    if (index1 !== (arr1.length - 1)) {
      index1++;
    } else if (index1 === (arr1.length - 1)) {
      index1 = 0;
      index2++;
      //concat(arr1, arr2, ++arrIndex, index1, index2++); // Not here dummy :P
    }
    concat(arr1, arr2, ++arrIndex, index1, index2++);
  }
  return arr;
}

Javascript - How to concatenate string values from two arrays of different sizes?

6 Answers6