PHP get previous array element knowing current array key

Question

I have an array with specific keys:

array(
    420 => array(...), 
    430 => array(...), 
    555 => array(...)
)

In my applicati

Answer 1

This is a simple solution for taking previous and next items, even if we are at the ends of the array.

<?php

$current_key; // the key of the item we want to search from

if (isset($array[$current_key+1])) 
{
  // get the next item if there is 
  $array_next = $array[$current_key+1];
} 
else 
{       
   // if not take the first (this means this is the end of the array)
  $array_next = $array[0];
}       

if (isset($array[$current_key-1])) 
{
   // get the previous item if there is
   $array_prev = $array[$current_key-1]; 
} 
else 
{   
  // if not take the last item (this means this is the beginning of the array)
  $array_prev = $array[count($array)-1];        
}

Answer 2

Expanding further on the solution of Luca Borrione and cenk, so that you can wrap around the end of the array in either direction, you may use:

function getAdjascentKey($key, $hash = array(), $increment) {
    $keys = array_keys($hash);    
    $found_index = array_search($key, $keys);
    if ($found_index === min(array_keys($keys)) && $increment === -1) {
        $found_index = max(array_keys($keys))+1;
    }
    if ($found_index === max(array_keys($keys)) && $increment === +1) {
        $found_index = min(array_keys($keys))-1;
    }       
    return $keys[$found_index+$increment];
}

Answer 3

You can iterate through the array in reverse and return the next iteration after finding the search value.

$found = false;
foreach(array_reverse($array, true) as $key=>$value) {
  if ($found) {
    print "$key => $value\n";
    break;
  } else if ($key == 555) {
    $found = true;
  }
}

http://ideone.com/2WqmC