array_unique inconsistent for simple arrays

Question

Why is it that

echo json_encode(array_unique([1,2,3,4,4]));

Outputs

[1,2,3,4]

And

echo json_encode(array_unique([1,2,3,3,4]));

Outputs

{"0":1,"1":2,"2":3,"4":4}

This has lead to some very odd bugs for me, and I simply cannot understand what's going on here. I just want to remove the duplicates from the array and have it returned as an array.

`array_unique()` does not reindex your array, so when you encode it in json it will include the keys in the output. — Rizier123, Jan 02 '17 at 00:42
http://stackoverflow.com/questions/30362192/why-php-function-json-encode-applied-for-a-not-associative-array-with-a-missin — Axalix, Jan 02 '17 at 00:42
@Rizier123 - but why not in the first case? Both arrays supplied as arguments have duplicate integers in them. — nickdnk, Jan 02 '17 at 00:43
@nickdnk Read: http://stackoverflow.com/a/11722121/3933332 there are many similar questions. — Rizier123, Jan 02 '17 at 00:43
@nickdnk what you need is this: `json_encode(array_values(array_unique([1,2,3,3,4])));` — Axalix, Jan 02 '17 at 00:44

score 3 · Accepted Answer · answered Jan 02 '17 at 00:45

array_unique([1,2,3,4,4]) returns:

array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [3]=>
  int(4)
}

Note that the keys are sequential

While array_unique([1,2,3,3,4])) returns:

array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [4]=>
  int(4)
}

Note the jump between the key 2 and the key 4.

Because of that - json_encode will omit the keys in the first array (and keep it as array object), while in the second array - the json_encode will look at your array as object and will keep the keys.

You can use array_values (to get the values and ignore the keys).

array_unique inconsistent for simple arrays

1 Answers1