Determine if a PHP array uses keys or indices [duplicate] - php

Question

This question already has answers here:
How to check if PHP array is associative or sequential?
(60 answers)
Closed 9 years ago.
How do I find out if a PHP array was built like this:
array('First', 'Second', 'Third');
Or like this:
array('first' => 'First', 'second' => 'Second', 'third' => 'Third');
???

Answer 1

I have these simple functions in my handy bag o' PHP tools:
function is_flat_array($ar) {
if (!is_array($ar))
return false;
$keys = array_keys($ar);
return array_keys($keys) === $keys;
}
function is_hash($ar) {
if (!is_array($ar))
return false;
$keys = array_keys($ar);
return array_keys($keys) !== $keys;
}
I've never tested its performance on large arrays. I mostly use it on arrays with 10 or fewer keys so it's not usually an issue. I suspect it will have better performance than comparing $keys to the generated range 0..count($array).

Answer 2

print_r($array);

Answer 3

There is no difference between
array('First', 'Second', 'Third');
and
array(0 => 'First', 1 => 'Second', 2 => 'Third');
The former just has implicit keys rather than you specifying them

Answer 4

programmatically, you can't. I suppose the only way to check in a case like yours would be to do something like:
foreach ($myarray as $key => $value) {
if ( is_numeric($key) ) {
echo "the array appears to use numeric (probably a case of the first)";
}
}
but this wouldn't detect the case where the array was built as $array = array(0 => "first", 1 => "second", etc);

Answer 5

function is_assoc($array) {
return (is_array($array)
&& (0 !== count(array_diff_key($array, array_keys(array_keys($array))))
|| count($array)==0)); // empty array is also associative
}
here's another
function is_assoc($array) {
if ( is_array($array) && ! empty($array) ) {
for ( $i = count($array) - 1; $i; $i-- ) {
if ( ! array_key_exists($i, $array) ) { return true; }
}
return ! array_key_exists(0, $array);
}
return false;
}
Gleefully swiped from the is_array comments on the PHP documentation site.

Answer 6

That's a little tricky, especially that this form array('First', 'Second', 'Third'); implicitly lets PHP generate keys values.
I guess a valid workaround would go something like:
function array_indexed( $array )
{
$last_k = -1;
foreach( $array as $k => $v )
{
if( $k != $last_k + 1 )
{
return false;
}
$last_k++;
}
return true;
}

Answer 7

If you have php > 5.1 and are only looking for 0-based arrays, you can shrink the code to
$stringKeys = array_diff_key($a, array_values($a));
$isZeroBased = empty($stringKeys);
I Hope this will help you
Jerome WAGNER

Answer 8

function isAssoc($arr)
{
return $arr !== array_values($arr);
}