Output only keys of nested array as string.

Question

I have a function that generates a multidimensional to represent a tree structure. A print_r of what it returns looks something like this:

Array (
    [A] => Array (
        [A1] =>
        [A2] =>
    )
    [B] => Array (
        [B1] => Array (
            [B1a] =>
        )
    )
)

What I need is a recursive function that output this in depth first order, like this:

A
  A1
  A2
B
  B1
    B1a

or just

A, A1, A2, B, B1, B1a

I have tried to solve this for hours now so please help me.

Donald · Accepted Answer · 2013-08-27 05:49:16Z

1

use recursive function eg:

<?php
$arr = array(
    'A'=>array(
        "A1"=>1,
        "A2"=>1,
        ),
        "B"=>array(
            "B1"=>array(
                "B2a"=>1,
                )
            ),
    );

function print_key($arr, $depth = 0){
    $pre_str = str_repeat("\t", $depth);
    foreach($arr as $k=>$v){
        echo $pre_str.$k."\n";
        if(is_array($v))
            print_key($v, $depth+1);
    }
}
print_key($arr);

answered Aug 27, 2013 at 5:49

Donald

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1 Comment

Donald Over a year ago

sometimes we get stuck，heng;)

Paul · Accepted Answer · 2013-08-26 22:34:04Z

1

You don't need to recursively scan the array, since print_r already does it for you. You could just call print_r and then parse the output:

preg_match_all('/^[^\[]*\[([^\]]*)\][^\]]*$/m', print_r($arr, true), $matches);
$result = implode(', ', $matches[1]);

echo $result; // A, A1, A2, B, B1, B1a

Demo

edited Aug 26, 2013 at 22:34

answered Aug 26, 2013 at 22:27

Paul

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1 Comment

user1823799 Over a year ago

Clever! I like the simplicity but i'll go for the recursive solution if i need to mark up the result or make other more complex changes later on. Still like this one though. Thanks!

Community · Accepted Answer · 2017-05-23 11:57:40Z

0

I realized I can just try to mimic the print_r function so I found a useable function here: php print_r nice table

edited May 23, 2017 at 11:57

CommunityBot

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answered Aug 26, 2013 at 22:16

user1823799

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