How to “flatten” a multi-dimensional array to simple one in PHP?

Question

It\'s probably beginner question but I\'m going through documentation for longer time already and I can\'t find any solution. I thought I could use implode for each dimensio

Answer 1

Given multi-dimensional array and converting it into one-dimensional, can be done by unsetting all values which are having arrays and saving them into first dimension, for example:

function _flatten_array($arr) {
  while ($arr) {
    list($key, $value) = each($arr); 
    is_array($value) ? $arr = $value : $out[$key] = $value;
    unset($arr[$key]);
  }
  return (array)$out;
}

Answer 2

A non-recursive solution (but order-destroying):

function flatten($ar) {
    $toflat = array($ar);
    $res = array();

    while (($r = array_shift($toflat)) !== NULL) {
        foreach ($r as $v) {
            if (is_array($v)) {
                $toflat[] = $v;
            } else {
                $res[] = $v;
            }
        }
    }

    return $res;
}

Answer 3

function flatten_array($array, $preserve_keys = 0, &$out = array()) {
    # Flatten a multidimensional array to one dimension, optionally preserving keys.
    #
    # $array - the array to flatten
    # $preserve_keys - 0 (default) to not preserve keys, 1 to preserve string keys only, 2 to preserve all keys
    # $out - internal use argument for recursion
    foreach($array as $key => $child)
        if(is_array($child))
            $out = flatten_array($child, $preserve_keys, $out);
        elseif($preserve_keys + is_string($key) > 1)
            $out[$key] = $child;
        else
            $out[] = $child;
    return $out;
}

Answer 4

I found a simple way to convert multilevel array into one. I use the function "http_build_query" which converts the array into a url string. Then, split the string with explode and decode the value.

Here is a sample.

$converted = http_build_query($data);
$rows = explode('&', $converted);
$output = array();
foreach($rows AS $k => $v){
   list($kk, $vv) = explode('=', $v);
   $output[ urldecode($kk) ] =  urldecode($vv);
}
return $output;

Answer 5

$array  = your array

$result = call_user_func_array('array_merge', $array);

echo "<pre>";
print_r($result);

REF: http://php.net/manual/en/function.call-user-func-array.php

Here is another solution (works with multi-dimensional array) :

function array_flatten($array) {

   $return = array();
   foreach ($array as $key => $value) {
       if (is_array($value)){ $return = array_merge($return, array_flatten($value));}
       else {$return[$key] = $value;}
   }
   return $return;

}

$array  = Your array

$result = array_flatten($array);

echo "<pre>";
print_r($result);

Answer 6

If you specifically have an array of arrays that doesn't go further than one level deep (a use case I find common) you can get away with array_merge and the splat operator.

<?php

$notFlat = [[1,2],[3,4]];
$flat = array_merge(...$notFlat);
var_dump($flat);

Output:

array(4) {
  [0]=>
  int(1)
  [1]=>
  int(2)
  [2]=>
  int(3)
  [3]=>
  int(4)
}

The splat operator effectively changes the array of arrays to a list of arrays as arguments for array_merge.