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I'm looking to create a function that checks an array for duplicate elements, and removes those elements only if the duplicate element is the same as the previous element. Let me give you a simple example:

The following array (in this case, the array will not be multi-dimensional) is as follows:

array('apple', 'apple', 'pear', 'orange', 'banana', 'apple', 'banana');

In this case, the remove duplicate array function, would return an array with the following elements:

array('apple', 'pear', 'orange', 'banana', 'apple', 'banana');

Note that there are still "duplicates" in the array. In case case, the first and second element, were duplicates (both "apple"), with one preceding the other. That said, there are three cases of "apple" found in the first array, but only one (in this case, the second element), was removed, because it was a duplicate of the previous element in the array. Going on those rules, while there are duplicates of "banana", since it isn't a duplicate of the previous array element, it isn't removed. Any ideas on a good function for this?

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4 Answers

up vote 2 down vote accepted

something like this perhaps:

function remove_adjacent_dups($arr) {
  $prev = null;
  $result = array();
  foreach( $arr as $val ) {
    if( $val !== $prev ) array_push($result, $val);
    $prev = $val;
  }
  return $result;
}
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This is exactly what I needed - thanks so much! – Brian Feb 21 '11 at 5:29
up vote 0 down vote

A version of this, depending on what you want to do with the keys.

$array = array('apple', 'apple', 'apple', 'apple', 'pear', 'orange', 'banana', 'apple', 'banana');
for ($i = 0; $i < count($array); $i++) {
    if ($array[$i] == $array[$i+1]) {
        unset($array[$i]);
    }
}
print_r($array);
//Array ( [3] => apple [4] => pear [5] => orange [6] => banana [7] => apple [8] => banana )
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1  
This worked as well, and was a bit different than a way that I accepted (which means I learned something new!). I accepted the other answer because 1.) It did what I needed and 2.) Was submitted first. Thanks so much for the help! – Brian Feb 21 '11 at 5:31
up vote 0 down vote

You could try this:

function removeDuplicates($dupeArray)
{
    $prevElement = NULL;

    foreach($dupeArray as $index => $element)
    {
        if ($prevElement && $prevElement == $element)
        {
            array_splice($dupeArray, $index, 1);
        }
        $prevElement = $element;
    }

    return $dupeArray;
}

$dupeArray = array('apple', 'apple', 'pear', 'orange', 'banana', 'apple', 'banana');
$newArray = removeDuplicates($dupeArray);

var_dump($newArray);
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up vote 0 down vote

I try array_walk ,but show Deprecated: Call-time pass-by-reference has been deprecated in 

    $foo = array('apple', 'apple', 'apple', 'apple', 'pear', 'orange', 'banana', 'apple', 'banana');
    function test ($v, $k, $data) {
        if (@$data[$k+1] == $v) {
            unset($data[$k]);
        }
    }
    array_walk($foo, 'test', &$foo);
    print_r($foo);
//how to solve "Deprecated" reporting
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