Get top x items from an array php - php

Question

array(10) { [0]=> int(5)
[1]=> int(8)
[2]=> int(2)
[3]=> int(0)
[4]=> int(1)
[5]=> int(9)
[6]=> int(1)
[7]=> int(0)
[8]=> int(5)
[9]=> int(4)
}
Ok, so I have an array as above. What I would like to do is get the top x items, change them into 1 and the rest into 0 without messing with the keys so that I can implode it back in the correct order. So if I want top 5, the result should be something like:
array(10) { [0]=> int(1)
[1]=> int(1)
[2]=> int(0)
[3]=> int(0)
[4]=> int(0)
[5]=> int(1)
[6]=> int(0)
[7]=> int(0)
[8]=> int(1)
[9]=> int(1)
}
I tried using sort, but I think it messes up the keys.
Any help would be appreciated. Thanks.

Answer 1

Uhm, I don't know If I understand question, but maybe:
for ($i = 0; $i < $topX; $i++)
$arr[$i] = (int)1;
for ($i = $topX+1;$i < count($arr); $i++)
$arr[$i] = (int)0;
Or add IF:
for ($i = 0; $i < count($arr); $i++)
$arr[$i] = ($arr[$i] < $maxVal) ? (int)1 : (int)0;

Answer 2

Well, I guess this is what you are looking for. I believe that the code is self-explain because I have comment all the important concept in the code.
<?php
function top(&$arr, $top, $start = 0)
{
if (count($arr) > $start) {
// count the number of element that larger
// than the element at start position
$count = 0;
for($i = $start + 1; $i < count($arr); $i++) {
if ($arr[$start] < $arr[$i]) $count++;
}
// if there are more than [$top] number of element
// that is larger than this element
// it cannot be in the [$top] largest number
if ($count >= $top) {
$arr[$start] = 0;
} else {
$arr[$start] = 1;
$top -= 1;
}
// continue to next element
top($arr, $top, $start + 1);
}
}
$arr = array(5, 8, 2, 0, 1, 9, 1, 0, 5, 4);
top($arr, 5);
var_dump($arr);
?>

Answer 3

asort() sort an array and maintain index association.

Answer 4

PHP has some pretty neat array-functions you can work with. Here's one approach:
<?php
function change_top_items($array, $top_x) {
// first, sort the values and preserve the keys
uasort($array, function($a, $b) {
if ($a == $b) return 0;
return ($a < $b) ? -1 : 1;
});
// put the top x values in an array
$compare = array_slice($array, -$top_x);
// now walk through the original array
$modified = array_map(function($value) use ($compare) {
// if the current value is in the top x array
// set it to 1, else set it to 0
return in_array($value, $compare) ? 1 : 0;
}, $array);
// now sort the modified array by keys again and return it
ksort($modified);
return $modified;
}
$a = [5, 8, 2, 0, 1, 9, 1, 0, 5, 4];
print_r(change_top_items($a, 5));
And that's pretty much it.
Output:
Array
(
[0] => 1
[1] => 1
[2] => 0
[3] => 0
[4] => 0
[5] => 1
[6] => 0
[7] => 0
[8] => 1
[9] => 1
)
Here's a working exapmple: http://3v4l.org/HI2EH - As you can also see there, I've used a syntax which is only valid for PHP 5.4+. This concerns the short array notation and the use of closures. But this code can easily be converted into a syntax of the previous PHP versions.