Changing values in array based on values in another array - php

Question

Here's an example in plain english of what I am trying to achieve:
if the number given is 4, then I want to add 1 to every value that is equal to or less than 4 into the corresponding index of another array. (hope that makes sense)
So my first array looks like this:
Array ( [0] => 5 [1] => 6 [2] => 7 [3] => 4 [4] => 3 [5] => 2 [6] => 9 [7] => 8 [8] => 1 [9] => 10 [10] => 11 [11] => 12 [12] => 13 [13] => 14 [14] => 15 [15] => 16 [16] => 17 [17] => 18 )
The second array looks like this:
Array ( [0] => 4 [1] => 3 [2] => 4 [3] => 4 [4] => 4 [5] => 5 [6] => 4 [7] => 4 [8] => 5 [9] => 4 [10] => 4 [11] => 5 [12] => 5 [13] => 4 [14] => 4 [15] => 4 [16] => 3 [17] => 3 )
And I am wanting the second array to look like this (after adding 1 to every value below 4 in the first array) so after the addition it would be
Array ( [0] => 4 [1] => 3 [2] => 4 [3] => 5 [4] => 5 [5] => 6 [6] => 4 [7] => 4 [8] => 6 [9] => 4 [10] => 4 [11] => 5 [12] => 5 [13] => 4 [14] => 4 [15] => 4 [16] => 3 [17] => 3 )
In which index 3,4,5,9 have changed.

Answer 1

I think you're looking for array_map
function increase( $m, $n )
{
if( $m < 4 )
{
return $n+1;
}
return $n
}
$arr1;
$arr2;
print_r( array_map("increase", $arr1, $arr2 ) );
Note: this will return a new array.

Answer 2

Using an array_walk
array_walk($arr2,function(&$v,$k) use($arr1) { if($arr1[$k]<=$v){ $v=$v+1;} });
Demo
[or]
A simple foreach will do
foreach($arr1 as $k=>$v)
{
if($v<=$arr2[$k])
{
$arr2[$k]=$arr2[$k]+1;
}
}
print_r($arr2);
Demo