PHP circular loop through array from n to n-1 element

Question

Let's say I have this array:

$myArray = array(a, b, c, d, e, f, g);

And I have a start indicator, $startpos, whose possible value can be any value from 0 to myArray's number of elements.

So if $startpos = 0, the desired print result would be a, b, c, d, e, f, g

if $startpos = 2, the desired print result would be c, d, e, f, g, a, b

if $startpos = 5, the desired print result would be f, g, a, b, c, d, e

I've been searching a php built-in or custom function through SO (similar question at Treat an array as circular array when selecting elements - PHP) and having a look to http://www.w3schools.com/php/php_ref_array.asp but I'm not getting the desired result. Anyone could please give me a suggestion?

Karim Harazin · Accepted Answer · 2016-11-28 10:36:31Z

5

You could use array_slice function with array_merge function as following :

$myArray = array('a', 'b', 'c', 'd', 'e', 'f', 'g');
$startpos = 2;


$output = array_merge(
                 array_slice($myArray,$startpos),
                 array_slice($myArray, 0, $startpos)
                    ); 
var_dump($output);

output:

array(7) {
  [0]=>
  string(1) "c"
  [1]=>
  string(1) "d"
  [2]=>
  string(1) "e"
  [3]=>
  string(1) "f"
  [4]=>
  string(1) "g"
  [5]=>
  string(1) "a"
  [6]=>
  string(1) "b"
}

answered Nov 28, 2016 at 10:36

Karim Harazin

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1 Comment

b1919676 Over a year ago

Thank you, buddy ;)

LF-DevJourney · Accepted Answer · 2016-11-28 11:01:15Z

2

demo

 <?php
      $myArray = array(a, b, c, d, e, f, g);
      $startpos = 3;
      $o = f($myArray, $startpos);
      echo json_encode($o);

      function f($myArray, $startpos)
      {
        $o = array();
        $l = count($myArray);
        array_walk($myArray, function($v, $k) use(&$o, $l, $startpos)
        {
          $o[($k + $l - $startpos) % $l] = $v;
        });
        ksort($o);
        return ($o);
      }

or use foreach method. demo

<?php
  $myArray = array(a, b, c, d, e, f, g);
  $startpos = 3;
  echo json_encode(f($myArray, $startpos));

  function f($myArray, $startpos)
  {
    $o = array();
    $l = count($myArray);
    foreach($myArray as $k => $v)
    {
      $o[($k + $l - $startpos) % $l] = $v;
    }
    ksort($o);
    return $o;
  }

outpur:["d","e","f","g","a","b","c"]

edited Nov 28, 2016 at 11:01

answered Nov 28, 2016 at 10:45

LF-DevJourney

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1 Comment

LF-DevJourney Over a year ago

@b1919676 my pleasure

Community · Accepted Answer · 2020-06-20 09:12:55Z

0

If you are looking for a simple logic you can go for the below codepiece:

$myArray = array('a', 'b', 'c', 'd', 'e', 'f', 'g');
$startpos = <any_position>;
$dummy_startpos = $startpos;  //keeping safe startpos for circular calculation
$initialpos = 0;

//loop to print element from startpos to end
while($dummy_startpos < count($myArray))
{
    echo $myArray[$dummy_startpos] . ' ';
    $dummy_startpos++;
}

//if startpos is not initial position
//start from first and print element till startpos
if($startpos > 0)
{
    while($elementleft < $startpos)
    {
        echo $myArray[$elementleft] . ' ';
        $elementleft++;
    }
}

Output :

$startpos : 3

o/p : d e f g a b c

$startpos : 0

o/p : a b c d e f g

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Nov 28, 2016 at 11:38

Subhra Jyoti Lahiri

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