How to create nested php arrays recursively?

问题

I have some data in this format:

one,one
two,two
sub_one,one
sub_two,two
sub_sub_one,sub_one
sub_sub_two,sub_two
sub_sub_sub_one,sub_sub_one
sub_sub_sub_two,sub_sub_two

Now I want to create nested arrays that contains that data, I coded this:

<?php
$lines[] = "one,one";
$lines[] = "two,two";
$lines[] = "sub_one,one";
$lines[] = "sub_two,two";
$lines[] = "sub_sub_one,sub_one";
$lines[] = "sub_sub_two,sub_two";
$lines[] = "sub_sub_sub_one,sub_sub_one";
$lines[] = "sub_sub_sub_two,sub_sub_two";

foreach($lines as $line)
{
    $tmp = explode(",", $line);
    $array[$tmp[1]][$tmp[0]] = $tmp[0];
}

foreach($array as $key => $value)
{
    foreach($array[$key] as $value2)
    {
        if(array_key_exists($value2, $array) && $value2 != $key)
        {           
            $array[$key][$value2] = $array[$value2];
            $unset[] = $value2;
        }
        else
        {
            unset($array[$key]);
        }
    }
}

foreach($unset as $un)
{
    unset($array[$un]);
}

print_r($array);
?>

But this only goes down to the 3rd level and no futher. The output looks like this:

Array
(
    [one] => Array
        (
            [sub_one] => Array
                (
                    [sub_sub_one] => sub_sub_one
                )

        )

    [two] => Array
        (
            [sub_two] => Array
                (
                    [sub_sub_two] => sub_sub_two
                )

        )

)

sub_sub_sub_one and sub_sub_sub_two are not in the output, how can I make my code recursive so no matter how many levels or relation exists in the data it will still work?

回答1:

Hmm from your code I understand that "one,one" means "one" is at top-level, and otherwise "a,b" means "a" is child of "b".

You could just convert all links into an associative array format, such that $links['a'] = 'sub_a' if sub_a is a child of 'a'. Then populate $nested recursively with the children of its deeper and deeper keys.

A sample code follows:

<?php

$nested = array();
$links = array();

// first, create a structure that contains the connections between elements
foreach ($lines as $line) {
  list($child, $parent) = explode(",", $line);
  if ($child == $parent) {
    $nested[$parent] = null;
  } else {
    // add it to the children of parent
    $links[$parent][] = $child;
  }
}

function process(&$arr) {
  global $links;
  foreach ($arr as $key => $value) {
    // no more children => stop recursion
    if (!array_key_exists($key, $links)) {
      $array[$key] = null;
      continue;
    }
    // insert its children
    $arr[$key] = array_flip($links[$key]);
    // recurse down
    process($arr[$key]);
  }
}

process($nested);

// $nested contains your m-dim array
print_r($nested);

?>

And the output:

Array
(
    [one] => Array
        (
            [sub_one] => Array
                (
                    [sub_sub_one] => Array
                        (
                            [sub_sub_sub_one] => 
                        )

                )

        )

    [two] => Array
        (
            [sub_two] => Array
                (
                    [sub_sub_two] => Array
                        (
                            [sub_sub_sub_two] => 
                        )

                )

        )

)

来源：https://stackoverflow.com/questions/5157243/how-to-create-nested-php-arrays-recursively