Differentiate an associative array from a regular array

Question

Without having to change the function signature, I'd like a PHP function to behave differently if given an associative array instead of a regular array.

Note: You can assume arrays are homogenous. E.g., array(1,2,"foo" => "bar") is not accepted and can be ignored.

function my_func(Array $foo){
  if (…) {
    echo "Found associative array";
  }
  else {
    echo "Found regular array";
  }
}


my_func(array("foo" => "bar", "hello" => "world"));
# => "Found associative array"

my_func(array(1,2,3,4));
# => "Found regular array"

Is this possible with PHP?

How would this function treat arrays that contain a mixture of numeric and associative indices (array(1, 2, 'foo' => 'bar', 3, 4, 'hello' => 'world'))? — BoltClock
– BoltClock, Commented Aug 12, 2010 at 19:47

Artefacto · Accepted Answer · 2010-08-12 19:52:38Z

6

Just check the type of any key:

function is_associative(array $a) {
    return is_string(key($a));
}

$a = array(1 => 0);
$a2 = array("a" => 0);

var_dump(is_associative($a)); //false
var_dump(is_associative($a2)); //true

answered Aug 12, 2010 at 19:52

Artefacto

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1 Comment

maček Over a year ago

I like this method best. Thanks :)

BoltClock · Accepted Answer · 2010-08-12 19:53:03Z

2

Assuming $foo is homogeneous, just check the type of one key and that's it.

<?php

function my_func(array $foo) {
    if (!is_int(key($foo))) {
        echo 'Found associative array';
    } else {
        echo 'Found indexed array';
    }
}

?>

answered Aug 12, 2010 at 19:53

BoltClock

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Comments

Peter Mortensen · Accepted Answer · 2024-06-01 22:56:19Z

2

You could use a check with array_values if your arrays are small and you don't care about the overhead (if they are large, this will be quite expensive as it requires copying the entire array just for the check, then disposing of it):

if ($array === array_values($array)) {}

If you care about memory, you could do:

function isAssociative(array $array) {
    $c = count($array);
    for ($i = 0; $i < $c; $i++) {
        if (!isset($array[$i])) {
            return true;
        }
    }
    return false;
}

Note that this will be fairly slow, since it involves iteration, but it should be much more memory efficient since it doesn't require any copying of the array.

Considering your homogeneous requirement, you can simply do this:

if (isset($array[0])) {
    // Non-Associative
} else {
    // Associative
}

But note that numerics are valid keys for an associative array. I assume you're talking about an associative array with string keys (which is what the above if will handle)...

edited Jun 1, 2024 at 22:56

Peter Mortensen

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answered Aug 12, 2010 at 19:50

ircmaxell

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2 Comments

Artefacto Over a year ago

Regarding your edit. You can have a numeric array that doesn't have the key 0, e.g. array(1 => null)

ircmaxell Over a year ago

Then it's not technically an array, it's still a hash table (and hence an associative array). Arrays would only have sequential numeric indexes from 0 to max...

Mchl · Accepted Answer · 2010-08-12 19:52:14Z

0

In the light of your comment Assume arrays are homogenous; no mixtures.: Just check if first (or last, or random) key is an integer or a string.

answered Aug 12, 2010 at 19:52

Mchl

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Comments

Marc B · Accepted Answer · 2010-08-12 19:52:33Z

0

This would be one way of doing it, by checking if there's any keys consisting of non-numeric values:

function my_func($arr) {
   $keys = array_keys($arr); // pull out all the keys into a new array
   $non_numeric = preg_grep('/\D/', $keys); // find any keys containing non-digits
   if (count($non_numeric) > 0) {
       return TRUE; // at least one non-numeric key, so it's not a "straight" array
   } else {
       return FALSE: // all keys are numeric, so most likely a straight array
   }
}

answered Aug 12, 2010 at 19:52

Marc B

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Comments

tamasd · Accepted Answer · 2010-08-12 20:01:24Z

0

function is_associative($array) {
  return count(array_keys($array)) != array_filter(array_keys($array), 'is_numeric');
}

answered Aug 12, 2010 at 20:01

tamasd

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