How to search by key=>value in a multidimensional array in PHP

Question 1

Is there any fast way to get all subarrays where a key value pair was found in a multidimensional array? I can't say how deep the array will be.

Simple example array:

$arr = array(0 => array(id=>1,name=>"cat 1"),
             1 => array(id=>2,name=>"cat 2"),
             2 => array(id=>3,name=>"cat 1")
);

When I search for key=name and value="cat 1" the function should return:

array(0 => array(id=>1,name=>"cat 1"),
      1 => array(id=>3,name=>"cat 1")
);

I guess the function has to be recursive to get down to the deepest level.

Question 2

Code:

function search($array, $key, $value)
{
    $results = array();

    if (is_array($array)) {
        if (isset($array[$key]) && $array[$key] == $value) {
            $results[] = $array;
        }

        foreach ($array as $subarray) {
            $results = array_merge($results, search($subarray, $key, $value));
        }
    }

    return $results;
}

$arr = array(0 => array(id=>1,name=>"cat 1"),
             1 => array(id=>2,name=>"cat 2"),
             2 => array(id=>3,name=>"cat 1"));

print_r(search($arr, 'name', 'cat 1'));

Output:

Array
(
    [0] => Array
        (
            [id] => 1
            [name] => cat 1
        )

    [1] => Array
        (
            [id] => 3
            [name] => cat 1
        )

)

If efficiency is important you could write it so all the recursive calls store their results in the same temporary $results array rather than merging arrays together, like so:

function search($array, $key, $value)
{
    $results = array();
    search_r($array, $key, $value, $results);
    return $results;
}

function search_r($array, $key, $value, &$results)
{
    if (!is_array($array)) {
        return;
    }

    if (isset($array[$key]) && $array[$key] == $value) {
        $results[] = $array;
    }

    foreach ($array as $subarray) {
        search_r($subarray, $key, $value, $results);
    }
}

The key there is that search_r takes its fourth parameter by reference rather than by value; the ampersand & is crucial.

FYI: If you have an older version of PHP then you have to specify the pass-by-reference part in the call to search_r rather than in its declaration. That is, the last line becomes search_r($subarray, $key, $value, &$results).

Question 3

Fiddled around for a bit, and I think I got it. I don't think there is any simpler way:

foreach ($array as $key=>$value) {
    preg_match("/[(.+)]/",$key,$match);
    $newKey = preg_replace("/[.+]/","",$key);
    $newArray[$newKey][$match[1]] = $value;
}

Where a print_r() of $newArray is as follows:

Array ( 
    [Template] => Array ( 
        [URL] => http://www.asdasdda.com 
        [UPC] => 5484548546314 
        ) 
    [Field] => Array ( 
        [value] => Test Example 
        [answer] => 20 
        ) 
    )

Question 4

I think (and you have confirmed) that you can represent your data as an XML structure. I this case, you can use XPath to find any branch in your data. Here is sample XML data inferred from your question:

<?xml version="1.0" encoding="utf-8" ?>
<stmt_echo>
    <subnodes>
        <exprs>
            <expr_constfetch>
                <subnodes>
                    <name>
                        <name>
                            <subnodes>
                                <parts>
                                    <part>true</part>
                                    <!-- more items -->
                                </parts>
                            </subnodes>
                        </name>
                    </name>
                </subnodes>
            </expr_constfetch>
            <!-- more items -->
        </exprs>
    </subnodes>
</stmt_echo>

And here is the PHP code to locate the node you mentioned:

$doc = new DOMDocument;
$doc->Load("test.xml");

$xpath = new DOMXPath($doc);
$nodes = $xpath->query("//subnodes/parts[part='true']");

foreach($nodes as $node) {
    dumpNodePath($node);
}

# Output
# /stmt_echo/subnodes/exprs/expr_constfetch/subnodes/name/name/subnodes/parts

function dumpNodePath($node) {
    $path = array($node->tagName);
    while ($node = $node->parentNode) {
        if ($node->nodeType != XML_DOCUMENT_NODE) {
            $path[] = $node->tagName;
        }
    }
    echo "/" . implode("/", array_reverse($path)) . "n";
}

Question 5

The idea is that you keep an auxiliary array with all the nodes (parent and child) you find. The values of this arrays are references that back your result.

This builds the tree in linear time (array_key_exists does a hash table lookup, which is on average O(1)):

//table contains (id, parent)
$orig = array(
    11 => 8,
    7 => 3,
    8 => 7,
    99 => 8,
    16 => 8,
);

$childrenTable = array();
$result = array();

foreach ($orig as $n => $p) {
    //parent was not seen before, put on root
    if (!array_key_exists($p, $childrenTable)) {
        $childrenTable[$p] = array();
        $result[$p] = &$childrenTable[$p];
    }
    //child was not seen before
    if (!array_key_exists($n, $childrenTable)) {
        $childrenTable[$n] = array();
    }

    //root node has a parent after all, relocate
    if (array_key_exists($n, $result)) {
        unset($result[$n]);
    }

    $childrenTable[$p][$n] = &$childrenTable[$n];
}
unset($childrenTable);

var_dump($result);

gives

array(1) {
  [3]=>
  array(1) {
    [7]=>
    array(1) {
      [8]=>
      array(3) {
        [11]=>
        array(0) {
        }
        [99]=>
        array(0) {
        }
        [16]=>
        array(0) {
        }
      }
    }
  }
}

EDIT: unset $childrenTable in the end to clear reference flags. In practice, you will probably want to do the operation inside a function anyway.

Question 6

Here you go.

Perl's multi-dimensional arrays are really arrays of references to the arrays. In perl a reference is just a scalar variable. So, when you are trying to print your whole array it prints out just that reference. You need to use the @{} to change the context of the scalar to array.

#!/usr/bin/perl
@array = ();
open(myfile,"sometext.txt");
while(<myfile>)
{
    chomp;
    push(@array,[split(" ")]);
}
close(myfile);
print @{@array[0]};

How to search by key=>value in a multidimensional array in PHP

Answers

php,arrays,search,recursion