How to detect duplicate values in PHP array?

Question

Hi!

I am working with a one dimensional array in PHP. I would like to detect the presence of duplicate values, then count the number of duplicate values and out put the results. For example, given the following array:

$array = array('apple', 'orange', 'pear', 'banana', 'apple',
   'pear', 'kiwi', 'kiwi', 'kiwi');

I would like to print:

apple (2)
orange
pear (2)
banana
kiwi (3)

Any advice on how to approach this problem?

Thanks.

Mike

Answer 1

use array_count_values

$array = array('apple', 'orange', 'pear', 'banana', 'apple',
'pear', 'kiwi', 'kiwi', 'kiwi');

print_r(array_count_values($array));

will output

Array
(
   [apple] => 2
   [orange] => 1
   [pear] => 2
   etc...
)

Answer 2

Stuff them into a map (pseudocode)

map[string -> int] $m
foreach($word in $array)
{
    if(!$m.contains($word))
        $m[$word] = 0;

    $m[$word] += 1;
}

Answer 3

Perhaps something like this (untested code but should give you an idea)?

$new = array();

foreach ($array as $value)
{
    if (isset($new[$value]))
        $new[$value]++;
    else
        $new[$value] = 1;
}

Then you'll get a new array with the values as keys and their value is the number of times they existed in the original array.

Answer 4

You could try turning that array into a associative array with the fruits as keys and the number of occurrences as values. Bit long-winded, but it looks like:

$array = array('apple', 'orange', 'pear', 'banana', 'apple',
   'pear', 'kiwi', 'kiwi', 'kiwi');
$new_array = array();
foreach ($array as $key => $value) {
    if(isset($new_array[$value]))
     $new_array[$value] += 1;
    else
     $new_array[$value] = 1;
}
foreach ($new_array as $fruit => $n) {
    echo $fruit;
    if($n > 1)
     echo "($n)";
    echo "<br />";
}

Answer 5

to get rid use array_unique. To detect if have any use count(array_unique) and compare to count(original array).

Answer 6

function array_not_unique( $a = array() )
{
  return array_diff_key( $a , array_unique( $a ) );
}