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Following on from our previous posts showing us lots about the array_filter() function are are now going to look at another function from the same family called array_udiff().


The array_udiff() function compares 2 or more arrays and returns elements from the first array based on a user defined function.

If the value should be included in our outputted array we must return the value 1 (for true) and if not we should return the value 0 (for false).

The syntax is as follows:

array_udiff( array1,  array2, array3, function );

We pass in our arrays first and then end with the name of our user defined function. Below is a basic example of this:

function udiffCompare( $value, $value2 )

if( $value === $value2 ) { return 1; } else { return 0; }


$array    =    array(

                    ‘value1’ => 1,
‘value2’ => 2,
‘value3’ => 3


$array2    =    array(

                    ‘value1‘ => 1,
value2‘ => 2,
value3‘ => 3,
value4‘ => 4,
value5‘ => 5


print_r( array_udiff( $array, $array2, ‘udiffCompare’ ) );

The output of the above would be:

    [value1] => 1
    [value2] => 2
    [value3] => 3

So, what is the above doing? Firstly our array is passed into the array_udiff() function, which in turn passes it to our custom callback function udiffCompare() which we defined above.

All our udiffCompare() function does is check if each arrays value passed to it are equal not and if it is it returns it as part of a new array, maintaining its array key value.

In the instance above you can see that the only similar values in the arrays are for the value “2” and as such this is all that is returned to our new array.

The beauty here is that you can make the call back function as simple or as complicated as your heart desires and is a great way to filter out our arrays in a way that other functions might just not accomplish.

Hopefully these functions will help you when filtering your arrays in your PHP Applications. If you would like any help with your PHP development or web projects then why not get in contact with us here at Network Intellect.

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