array_unique inconsistent for simple arrays [duplicate]

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
– Rizier123, Commented Jan 2, 2017 at 0:42
@Rizier123 - but why not in the first case? Both arrays supplied as arguments have duplicate integers in them. — nickdnk
– nickdnk, Commented Jan 2, 2017 at 0:43
@nickdnk Read: stackoverflow.com/a/11722121/3933332 there are many similar questions. — Rizier123
– Rizier123, Commented Jan 2, 2017 at 0:43
@nickdnk what you need is this: json_encode(array_values(array_unique([1,2,3,3,4]))); — Axalix
– Axalix, Commented Jan 2, 2017 at 0:44

Dekel · Accepted Answer · 2017-01-02 00:45:55Z

3

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).

answered Jan 2, 2017 at 0:45

Dekel

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