array_unique does not sort a simple string array

Question

According to the PHP documentation, array_unique removes duplicate values and sorts the values treated as string at first.

When you take the following snippet in mind:

// define a simple array of strings, unordered
$brands = [ "BMW", "Audi", "BMW", "Chrysler", "Daewoo"];

// distinct the values, and sort them
echo array_unique($brands, SORT_STRING);

I would expect the output to be:

expected: {"0":"Audi","1":"BMW","3":"Chrysler","4":"Daewoo"}
actual  : {"0":"BMW","1":"Audi","3":"Chrysler","4":"Daewoo"}

The question is: why doesn't array_unique sort these values? Changing the sort_flags parameter to any of the four alternatives, or leaving it empty, has no effect either.

According to other SO questions, like "Why does array unique sort the values" I'm probably missing something obvious here. Also, using array_values(array_unique($brands)), as stated as an answer in this question doesn't seem to work either.

Update: As stated in the useful comments and answers, the sort_flags parameter is actually an inner compare behavior, or equality operator, sort of speak.

array_unique does not sort array elements. It just removes duplicate values from array. The manual is only mentioning the sorts word regarding to internal (temporary) array processing. It doesn't mean real array sorting — hindmost
– hindmost, Commented Aug 23, 2014 at 8:45
So, actually 'sort_flag' should really be interpreted as 'compare_behaviour'? If so, the naming convention and the forementioned posts confused me on this part. — Juliën
– Juliën, Commented Aug 23, 2014 at 8:47

Dmitry Bezik · Accepted Answer · 2014-08-23 10:10:05Z

3

In manual they mean that values group by value and first key taken for eacj duplicated value.

you need something like this

$brands = array_unique($brands);
sort($brands);

SORT_STRING - is default

edited Aug 23, 2014 at 10:10

answered Aug 23, 2014 at 8:47

Dmitry Bezik

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3 Comments

deceze Over a year ago

You cannot call sort this way, BTW.

Tom Fenech Over a year ago

sort doesn't return the sorted array, it returns a boolean indicating whether it was successful. It relies on the array being passed by reference, which I don't think is compatible with using the result of a function.

Nightwhistle Over a year ago

this works though: $brands = array_unique($brands); sort($brands);

Community · Accepted Answer · 2017-05-23 11:52:14Z

2

The documentation simply specifies how the algorithm is working internally to achieve its purpose. Why and how is well explained in the other question. It does not say that the returned result will be sorted as well. Sorting is outside the scope of this function and probably actually undesired most of the time.

For completeness, this is how'd you unique (is that a verb?) and sort the array:

$array = array_unique($array);
sort($array);

edited May 23, 2017 at 11:52

CommunityBot

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answered Aug 23, 2014 at 8:48

deceze♦

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7 Comments

Tom Fenech Over a year ago

There's no harm in adding a quick two line example to make your answer complete.

deceze Over a year ago

@Tom An example of what exactly?

Tom Fenech Over a year ago

An example of how you would obtain the sorted, unique values of an array.

deceze Over a year ago

I thought I was just answering the question why array_unique _doesn't_ sort. I'd think the OP could do it manually if they wanted...?! :)

Tom Fenech Over a year ago

For the record, it's not a verb :)

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