php - print even and (sorted) odd numbers of an array

Question

I have an array given below

$array = array(50,51,52,53,54,55,56,57,58,59);

I am trying to print the values of array while even numbers will remain in same order and the odd numbers are sorted i.e. 59,57,55,53,51

The output should be like

50,59,52,57,54,55,56,53,58,51

I've separated the even and odd numbers in two diff variables. how should i proceed further ?

here is my code

  $even= "";
  $odd= "";

for($i=50;$i<=59;$i++)
{
    if($i%2==0)
    {
        $even.=$i.",";
    }else $odd.=$i.","; 
}   
echo $even.$odd;

Something like this should work for you: 3v4l.org/MRu43 basically you get the odd values out of the array and sort them. After that you just replace the odd values from your original array with the sorted odd values. — Rizier123
– Rizier123, Commented Aug 22, 2016 at 18:18

Charlotte Dunois · Accepted Answer · 2016-08-22 18:23:42Z

3

Instead of pushing the evens and odds into a string, push them each into an array, sort the array with the odds in reverse and then loop through one of them (preferably through the even array) and add the even and the odd to a new array.

This is how I've done it:

$array = array(50,51,52,53,54,55,56,57,58,59);
$odds = array();
$even = array();
foreach($array as $val) {
    if($val % 2 == 0) {
        $even[] = $val;
    } else {
        $odds[] = $val;
    }
}

sort($even);
rsort($odds);

$array = array();
foreach($even as $key => $val) {
    $array[] = $val;
    if(isset($odds[$key])) {
        $array[] = $odds[$key];
    }
}

https://3v4l.org/2hW6T

But you should be cautious if you have less even than odd numbers, as the loop will finish before all odds are added. You can check for that either before or after you've filled the new array. If you check after filling the new array, you can use array_diff and array_merge to add the missing odds to the new array.

http://php.net/array_diff http://php.net/array_merge

edited Aug 22, 2016 at 18:23

answered Aug 22, 2016 at 18:12

Charlotte Dunois

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6 Comments

Rizier123 Over a year ago

This will only work as long as odd and even values are in alternating order.

Charlotte Dunois Over a year ago

@Rizier123 Why should it only work if they're in alternating order?

Rizier123 Over a year ago

@CharlotteDunois For example if there are two odd or even values besides each other in the array it will break: 3v4l.org/lN4aj

Charlotte Dunois Over a year ago

@Rizier123 I don't see anything broken. It's in the intended order.

mickmackusa Jan 20 at 20:35

This answer is only appropriate if the input array alternates from even and odd every time. The loop after sorting is blindly zippering the values back together.

|

Dharman · Accepted Answer · 2021-12-24 09:28:39Z

0

Following code will run as per the odd number count. There won't be any loop count issue.

  function oddNumber($num){
    return $num % 2 == 1;
  }

  $givenArray = array(50, 51, 52, 53, 54, 55, 56, 57, 58, 59);

  $oddArray = array_filter($givenArray, "oddNumber");

  rsort($oddArray);

  $finalArray = array();
  $oddCount = 0;
  foreach($givenArray as $num){
      if(oddNumber($num)){    
          $finalArray[] = $oddArray[$oddCount];
          ++$oddCount;
      }else{
          $finalArray[] = $num;    
      }
  }

  print_r($finalArray);

edited Dec 24, 2021 at 9:28

Dharman♦

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answered Dec 24, 2021 at 9:23

alwayS_U

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Comments

mickmackusa · Accepted Answer · 2025-01-20 21:17:17Z

Isolate the odds values in a new array, preserve the keys of those odds values, sort the odds values descending, reinsert the sorted values into the original array at the cached keys. Demo

$odds = [];
foreach ($array as $i => $v) {
    if ($v & 1) {
        $odds[$i] = $v;
    }
}
$keys = array_keys($odds);
rsort($odds);
foreach ($keys as $i => $k) {
    $array[$k] = $odds[$i];
}
var_export($array);

Or this variation. Demo

$odds = [];
foreach ($array as $i => $v) {
    if ($v & 1) {
        $keys[] = $i;
        $odds[] = $v;
    }
}
rsort($odds);
var_export(
    array_replace(
        $array,
        array_combine($keys, $odds)
    )
);

To spare you the effort of trying to sort values directly by reference, THIS WILL NOT provide the desired mutation:

$odds = [];
foreach ($array as &$v) {
    if ($v & 1) {
        $odds[] =& $v;
    }
}
rsort($odds);
var_export($array);

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