get the percentage of similarity of two arrays in php

Question

I need to take two arrays and come up with a percent of similarity. ie:

array( 0=>'1' , 1=>'2' , 2=>'6' , 3=>array(0=>1))

vers

array( 0=>'1' , 1=>'45' , 2=>'6' , 3=>array(0=>1))

Where I would think that the % is 75

or

array( 0=>'1' , 1=>'2' , 2=>'6' , 3=>array(0=>'1'))

vers

array( 0=>'1' , 1=>'2' , 2=>'6' , 3=>array(0=>'55'))

Not sure how to approach this.. just need to end up with a workable float percent. Thank you .

Answer 1

Here's how I tackled this problem recently:

$array1 = array('item1','item2','item3','item4','item5');
$array2 = array('item1','item4','item6','item7','item8','item9','item10');

// returns array containing only items that appear in both arrays
$matches = array_intersect($array1,$array2);

// calculate 'similarity' of array 2 to array 1
// if you want to calculate the inverse, the 'similarity' of array 1
// to array 2, replace $array1 with $array2 below

$a = round(count($matches));

$b = count($array1);

$similarity = $a/$b*100;

echo 'SIMILARITY: ' . $similarity . '%';

// i.e., SIMILARITY: 40%
// (2 of 5 items in array1 have matches in array2 = 40%)

Answer 2

Assuming both arrays are the same length, you can iterate through and see which values are the same for the keys, for example:

<?php
$a = array(1,2,3,4);
$b = array(1,2,4,4);
$c = 0;
foreach ($a as $k=>$v) {
    if ($v == $b[$k]) $c++;
}
echo ($c/count($a))*100;
// outputs 75
?>

Or just checking whether they contain similar items using in_array.

<?php
$a = array(1,2,3);
$b = array(1,2,4);
$c = 0;
foreach ($a as $i) {
    if (in_array($i,$b)) $c++;
}
echo ($c/count($a))*100;
// outputs 66.66...
?>