add to array if it isn't there already

Question

How do I add elements to an array only if they aren\'t in there already? I have the following:

$a=array();
// organize the array
foreach($array as $k=>$v)         


        

Answer 1

You should use the PHP function in_array (see http://php.net/manual/en/function.in-array.php).

if (!in_array($value, $array))
{
    $array[] = $value; 
}

This is what the documentation says about in_array:

Returns TRUE if needle is found in the array, FALSE otherwise.

Answer 2

Easy to write, but not the most effective one:

$array = array_unique(array_merge($array, $array_to_append));

This one is probably faster:

$array = array_merge($array, array_diff($array_to_append, $array));

Answer 3

if (!in_array($value, $a))
  $a[]=$value;

Answer 4

Try adding as key instead of value:

Adding an entry

function addEntry($entry) {
    $this->entries[$entry] = true;
}

Getting all entries

function getEntries() {
    return array_keys($this->enties);
}

Answer 5

You'd have to check each value against in_array:

$a=array();
// organize the array by cusip
foreach($array as $k=>$v){
    foreach($v as $key=>$value){
        if(!in_array($value, $a)){
        $a[]=$value;
        }
    }
}

Answer 6

if (!in_array(...))  
  array_push(..)