Finding an array of arrays... inside another array

Question

I'm dealing with 'arrays of arrays' and trying to test if all 'sets' contained in the second array are present in the first array.

var arr = [['Netherlands','PP3a'],['Austria','PP16a'],['Estonia','PP3a'],['Luxembourg','PP3a'],['Belgium','PP3a']];

var n   = [['Luxembourg','PP3a'],['Netherlands','PP3a'],['Belgium','PP3a']];

In my example https://jsfiddle.net/mnb8jddw/ they clearly are present, but the code (which incidentally seems to work with numbers), reads false. I've obviously got myself confused and would really appreciate some help as I suspect I'm taking the wrong approach.

var arr = [
  ['Netherlands', 'PP3a'],
  ['Austria', 'PP16a'],
  ['Estonia', 'PP3a'],
  ['Luxembourg', 'PP3a'],
  ['Belgium', 'PP3a']
];
var n = [
  ['Luxembourg', 'PP3a'],
  ['Netherlands', 'PP3a'],
  ['Belgium', 'PP3a']
];

function searchForArray(haystack, needle) {
  var i, j, current;
  for (var i in haystack) {
    if (needle.length === haystack[i].length) {
      current = haystack[i];
      for (j = 0; j < needle.length && needle[j] === current[j]; ++j);
      if (j === needle.length)
        return i;
    }
  }
  return -1;
}

console.log(searchForArray(arr, n)); // -1 = false

According to the code, the needle should be one subelement of n. For eg, searchForArray(arr,n[0]); would returns 3. — Alexis Côté
– Alexis Côté, Commented Sep 9, 2017 at 17:46
what index your function should return? the elements you search do not exist in that order — AndreaBogazzi
– AndreaBogazzi, Commented Sep 9, 2017 at 18:03

cl3m · Accepted Answer · 2017-09-09 17:53:27Z

1

I'm not sure that it is the answer you are looking for, but if you are looking for a quick and dirty solution, you could try something like this:

const lookup = (ar, sets) => {
  // concatenate each entry in the searched array
  const _hashed = ar.map(i => i.join(''))
  return sets.every((set) => {
    // contatenate each entry to look for
    const _set = set.join('')
    // does the searched array contain the concatenated string?
    return _hashed.indexOf(_set) > -1
  })
}

console.log(lookup(arr, n)) // => true

Note that the order of the elements matters (ie: ['Luxembourg', 'PP3a'] will match, but ['PP3a', 'Luxembourg'] won't)

See updated fiddle

answered Sep 9, 2017 at 17:53

cl3m

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2 Comments

Silverburch Over a year ago

I'm really not sure why you call this 'Q&D'. It does the job brilliantly and I much appreciate your help!

cl3m Over a year ago

Q&D because map and every methods are not really optimized for speed, and, as stated, it won't fit every use cases. You may consider sorting the strings (.sort((a, b) => a.localeCompare(b))) if order matters!

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