Getting Nested Values From Associative Array

Question

This is sort of a general implementation question. If I have an arbitrarily deep array, and I do not know before hand what the keys will be, what is the best way to access the values at specific paths of the associative array? For example, given the array:

array(
    'great-grandparent' = array(
        'grandparent' = array(
             'parent' = array(
                  'child' = 'value';
              ),
              'parent2' = 'value';
         ),
         'grandparent2' = 'value';
    )
);

Whats the best way to access the value at $array['great-grandparent']['grandparent']['parent']['child'] keeping in mind that I don't know the keys beforehand. I have used eval to construct the above syntax as a string with variable names and then eval'd the string to get the data. But eval is slow and I was hoping for something faster. Something like $class->getConfigValue('great-grandparent/grandparent/'.$parent.'/child'); that would return 'value'

Example of Eval Code

public function getValue($path, $withAttributes=false) {
        $path = explode('/', $path);
        $rs = '$r = $this->_data[\'config\']';
        foreach ($path as $attr) {
            $rs .= '[\'' . $attr . '\']';
        }
        $rs .= ';';
        $r = null;
        @eval($rs);
        if($withAttributes === false) {
            $r = $this->_removeAttributes($r);
        }
        return $r;
    }

added the eval code. It's basically taking a / delimited path and turning it into array access syntax then evaling. — chris
– chris, Commented Mar 25, 2011 at 21:50
yes. ha i need more characters for a comment so here they are — chris
– chris, Commented Mar 25, 2011 at 21:52

Julien Roncaglia · Accepted Answer · 2011-03-25 22:44:50Z

2

I don't know about the potential speed but you don't need to use eval to do a search like that :

  $conf = array(
      'great-grandparent' => array(
          'grandparent' => array(
               'parent' => array(
                    'child' => 'value searched'
                ),
                'parent2' => 'value'
           ),
           'grandparent2' => 'value'
      )
  );

  $path = 'great-grandparent/grandparent/parent/child';
  $path = explode('/', $path);

  $result = $conf;

  while(count($path) > 0) {
      $part = array_shift($path);

      if (is_array($result) && array_key_exists($part, $result)) {
          $result = $result[$part];
      } else {
          $result = null;
          break;
      }
  }

  echo $result;

edited Mar 25, 2011 at 22:44

answered Mar 25, 2011 at 22:23

Julien Roncaglia

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2 Comments

Nick Weaver Over a year ago

+1 Been working myself on an algorithm :) Your solution does not work 100% correct I think, try a path like this great-grandparent/grandparent2/parent2 I get a v as output which should not be correct.

Julien Roncaglia Over a year ago

@Nick Weaver: Oh i didn't manage the error cases in my sample, added it now.

Nick Weaver · Accepted Answer · 2011-03-25 22:39:41Z

0

Here we go, my solution:

$tree = array(
    'great-grandparent' => array(
        'grandparent' => array(
             'parent' => array(
                  'child' => 'value1'
              ),
              'parent2' => 'value2'
         ),
         'grandparent2' => 'value3'
    )
);

$pathParts = explode('/','great-grandparent/grandparent/parent/child');
$pathParts = array_reverse($pathParts);

echo retrieveValueForPath($tree, $pathParts);

function retrieveValueForPath($node, $pathParts)  {
    foreach($node as $key => $value) {
        if(($key == $pathParts[count($pathParts)-1]) && (count($pathParts)==1)) {
            return $value;
        }       

        if($key == $pathParts[count($pathParts)-1]) {
            array_pop($pathParts);
        }

        if(is_array($value)) {
            $result = retrieveValueForPath($value, $pathParts);
        }
    }

    return $result;
}

edited Mar 25, 2011 at 22:39

answered Mar 25, 2011 at 21:54

Nick Weaver

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2 Comments

chris Over a year ago

I had an xml implementation as well but xml is so slow to parse, i thought someone on here might have a simple solution I overlooked. The problem with xml is the complexity involved when merging nodes and node inheritance

chris Over a year ago

The parse_ini returns an array which I have already created so no need to get an array from an ini file

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