How to handle very large arrays in php?

Question

I have this code block.

$input = 4;
$list_N = array('0', '1');
for($n=1; $n<=$input; $n++) {

    if($n%2 == 0) {
        $c++;
    }

    $reverse_list_N = array_reverse($list_N);

    $A = array();
    $B = array();

    for($i=0; $i<count($list_N); $i++) {
        $A[] = '0' . $list_N[$i];
        $B[] = '1' . $reverse_list_N[$i];
    }

    $list_N = array_merge($A[], $B[]);

    if($n == 1) {
        $list_N = array('0', '1');
    }
}
$array_sliced = array_slice($list_N, -1*$input, $input);
for($i=0; $i<count($array_sliced); $i++) {
    $output = implode("\n", $array_sliced);
}
echo "<pre>"; print_r($output); echo "</pre>";

What this code does, it generates the following data (starting with (0,1)):

0,1
00, 01, 11, 10
000, 001, 011, 010, 110, 111, 101, 100
....... and so on

When the $input = 4;conclusion:

1010
1011
1001
1000

And as you can see, after each cycle, the elements in the array are $list_Ndoubled than the previous ones. And with this step, if $input = 25;, then the array would have 33554432elements that are very huge. And in this I could not find a solution. When $input = 60, I get this error

Fatal error: Allowed memory size of 134217728 bytes exhausted (tried to allocate 36 bytes)

in this line

$list_N = array_merge($A, $B);

Even setting the memory limit to 2G did not solve it. So, how do I optimize my code for the same amount of memory. Or is there another solution?

Update: Use the following steps to generate data.

$list_N is an array
$reverse_list is the reverse of $list_N
0 is appended in the beginning of every element in the $list_N array and stored in $A
1 is appended in the beginning of every element in the $reverse_list_N array and stored in $B
Array $A and array $B are merged and is stored in $list_N.
The main loop runs for $input number of times and the last $input number of elements are displayed from the final array.

Answer 1

Decision

SplFixedArray!

:

A SplFixedArray -

37% ""

SplFixedArray . , .

:

:

$startMemory = memory_get_usage();
$array = new SplFixedArray(100000);
for ($i = 0; $i < 100000; ++$i) {
    $array[$i] = $i;
}
echo memory_get_usage() - $startMemory, ' bytes';

:

: http://nikic.imtqy.com/2011/12/12/How-big-are-PHP-arrays-really-Hint-BIG.html

---

Messier:

, , , . , :

ini_set('memory_limit', '-1')

:

http://php.net/memory_limit

Answer 2

@tadman . . , 65, , 1 32 Exabytes ( , script).

(, , script):

// , > 1

fscanf(STDIN, "%d\n", $target);

$base=["0","1"];
$root=["0","1"];

$newArr=$base;
for($i=1;$i<7;$i++)//pre-initialize root array
  $newArr=genNextArray($newArr);

//echo "-----------\n";

//print_r($root);

//we're ready to display the output now based on the root array elements
displayNBits($target);

function displayNBits($target)
{
  global $root;
  $arr=array();

  for($i=0;$i<$target;$i++)
  {
    $elem=str_pad($root[$i],$target,"0",STR_PAD_LEFT);
    $elem[0]="1";
    $arr[]=$elem;

  }

  $arr=array_reverse($arr);

  for($i=0;$i<count($arr);$i++)
    echo $arr[$i]."\n";

  //print_r($arr);
}

function genNextArray($arr)
{
  global $root;

  $newArr= array(count($arr)*2);

  $ni=0;

  //0 prefix (left to right sweep)
  for($i=0;$i<count($arr);$i++)
  {
    $newArr[$ni]="0".$arr[$i];
    $ni++;
  }

  //1 prefix (right to left sweep)
  for($i=count($arr)-1;$i>=0;$i--)
  {
    $newArr[$ni]="1".$arr[$i];
    $root[]=$newArr[$ni];
    $ni++;
  }

  return $newArr;
}

Answer 3

If there is no way to make your array more compact or you cannot use other methods such as pagination, you can simply increase the memory limit :

ini_set('memory_limit','256M');

This will increase the memory limit to 256 megabytes until the request is completed. The default is 128M.