PHP阵列数组独特

Question

I have an array of arrays as following:

$a = array(
  1 => array("sport", "geo"),
  2 => array("sport", "geo", "history"),
  3 => array("geo", "history"),
  4 => array("golf", "sport"),
  ...
);

From that I need to get keys, in such a way so that values are unique. So from that I would need to get something like:

$b = array( 1, 3, 4 );

$a[2] would be cut out, since it has the same values as $a[1], but since $a[2] is not there, $a[3] is fine.

If some values get completely cut out, that's fine. I will have 30+ keys, from which I need to get 10, which have unique values.

Key is a question ID, and values are tags.

I want to get 10 questions, which are different from each other (so that I don't get 10 questions about Sport).

I tried array_unique(), but that just returns this:

Array ( 
  [1] => Array ( 
    [0] => sport 
    [1] => geo 
  )
) 

which doesn't seem to help much.

Can you guys point me towards something that could help me?

I guess I could try to list all possible categories, make that array unique, sort it by random. I would need to preserve Keys, but Keys are unique...

Answer 1

Just iterate through the initial array of questions, every time save the value (array of tags) to another temporary array with checking if actual tags already exists in temporary array - if not add the question to temporary array, if exists go next. Do it until you have 10 questions in your temporary array, if you finish the question array without already having 10 questions - repeat the iteration but this time add other questions even if the tags are repeating - until you have 10.