Count the number of numeric keys in an array

Question

I'm using PHP 5.6, and I have the following array:

Array (
    [0] => Array (
            [id] => 1
            [name] => James
        )
    [1] => Array (
            [id] => 2
            [name] => Tim
            [children] => Array (
                    [0] => Array (
                            [id] => 4
                            [name] => Sam
                        )
                    [1] => Array (
                            [id] => 5
                            [name] => Florence
                        )
                )
        )
    [2] => Array (
            [id] => 3
            [name] => Stephen
        )
)

I'm trying to find a neat and fast way to count the number of people, which is the same as counting the number of numeric keys, which should be 5.

echo count($myarray); // 3 (only first level)
echo count($myarray, COUNT_RECURSIVE); // 16 (every key/value)

Is there a good way to do this with built-in PHP functions, or do I need to traverse the whole multidimensional array and count them manually..?

EDIT My array could end up being 1,000+ people (or more), with many many levels (an unknown number of levels).

Is there a reason that you can't just walk through it with a for loop? — kainaw
– kainaw, Commented Jan 13, 2016 at 14:49
@kainaw, a for loop would have to recurs through the array many time, like the function in my answer :P — anon
– anon, Commented Jan 13, 2016 at 14:50
I could, but my array could end up being 1,000+ people, with many many levels (an unknown number of levels), so I'm looking for a neater way. — Stephen Last
– Stephen Last, Commented Jan 13, 2016 at 14:52
@CrusaderLtd, has my answer helped you at all or do you need something else? — anon
– anon, Commented Jan 13, 2016 at 14:56
count() just counts keys. it doesn't care WHAT those keys are, or they represent. it has no filtering functions. if you want to count only numeric keys, you'll have to build that yourself. e.g. preg_grep('/^\d+$/', array_keys($arr)), but that doesn't do recursion. — Marc B
– Marc B, Commented Jan 13, 2016 at 15:05

Mike · Accepted Answer · 2016-01-16 18:15:13Z

2

It is important to note that, even if there were a PHP built-in (such as count($myarray, COUNT_RECURSIVE_NUMERIC);) internally, it would still be traversing the whole array, recursively. If you are worried about Out Of Memory errors, try pass-by-reference, which will not copy the array or the array items:

define('COUNT_RECURSIVE', 1);

function count_numeric_keys(&$array, $flags = 0) {
    $count = 0;
    foreach ($array as $key => $value) {
        $count += (int) (is_numeric($key));
        if ($flags & COUNT_RECURSIVE && is_array($value)) {
            $count += count_numeric_keys($value, $flags);
        }
    }
    return (int) $count;
}

$count = count_numeric_keys($array, COUNT_RECURSIVE);

Mayhaps?

Comparison with non-pass-by-reference, type-hint, and small benchmark:

define('COUNT_RECURSIVE', 1);

function count_numeric_keys(Array &$array, $flags = 0) {
    $count = 0;
    foreach ($array as $key => $value) {
        $count += (int) (is_numeric($key));
        if ($flags & COUNT_RECURSIVE && is_array($value)) {
            $count += count_numeric_keys($value, $flags);
        }
    }
    return (int) $count;
}

function count_numeric_keys_np(Array $array, $flags = 0) {
    $count = 0;
    foreach ($array as $key => $value) {
        $count += (int) (is_numeric($key));
        if ($flags & COUNT_RECURSIVE && is_array($value)) {
            $count += count_numeric_keys_np($value, $flags);
        }
    }
    return (int) $count;
}

$tpl_array = array(
    1=>"one",
    "two"=>"two",
    3=>array(
        1=>1,
        "two"=>2
    )
);

// Fill the array with both numeric and non-numeric
$array = array();
for($i = 1000; $i > 0; $i--) {
    $array[] = $tpl_array;
}

for($i = 1000; $i > 0; $i--) {
    $array["not a number $i"] = $tpl_array;
}

echo "Pre Memory: ".memory_get_usage(TRUE).PHP_EOL;
echo "Count: ".count_numeric_keys($array, COUNT_RECURSIVE).PHP_EOL;
echo "Reference Memory: ".memory_get_usage(TRUE)." current, ".memory_get_peak_usage(TRUE)." peak.\n";

count_numeric_keys_np($array, COUNT_RECURSIVE);
echo "No-Reference Memory: ".memory_get_usage(TRUE)." current, ".memory_get_peak_usage(TRUE)." peak.\n";

View it on IDEONE here.

ODDLY, having a reference on $value, like foreach($array as $key => &value) {} actually increased memory usage. Bizarre...

edited Jan 16, 2016 at 18:15

answered Jan 13, 2016 at 15:15

Mike

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4 Comments

I wrestled a bear once. Over a year ago

pass by ref.. you should do the same with the $count var and just do $count++;

Stephen Last Over a year ago

Thanks Mike... Any mileage is using array_walk rather than foreach..?

Mike Over a year ago

Less overhead in foreach, array_walk is cleaner for applying strictly callbacks, also, it would prevent the counting bit without additional overhead.

Mike Over a year ago

Just a note, I re-edited my edit. The Flag adds minimal overhead, and I added a type-hint. IDEOne is up to date.

score 1 · Accepted Answer · 2016-01-13 15:10:01Z

1

I just created this recursive function to do this for ya :P

function countNumericKeys($array)
{
    $count = 0;
    foreach ($array as $key => $value)
    {
        if (is_numeric($key))
        {
            $count ++;
        }
        if (is_array($value))
        {
            $count += countNumericKeys($value);
        }
    }
    return $count;
}

// Test it!

$array = [
    1=>"one",
    "two"=>"two",
    3=>[
        1=>1,
        "two"=>2
    ]
];

print countNumericKeys($array); // Output: 3, correct (in this case at least)!

Shortened the code so it uses ternary operators instead of the ifs that it was :P

function simpleCountNumericKeys($array)
{
    $count = 0;
    foreach ($array as $key => $value)
    {
        $count += is_numeric($key) ? 1 : 0;
        $count += is_array($value) ? simpleCountNumericKeys($value) : 0;
    }
    return $count;
}

TEST USING array_keys -- only gets the top level keys of the array

function countArrayKeysNumeric($array)
{
    $count = 0;
    $keys = array_keys($array);
    foreach ($keys as $key) $count += is_numeric($key) ? 1 :0;
    return $count;
}

$array = [
    1=>"one",
    "two"=>"two",
    3=>[
        1=>1,
        "two"=>2
    ]
];

print countArrayKeysNumeric($array);

Prints 2... :(

edited Jan 13, 2016 at 15:10

answered Jan 13, 2016 at 14:49

anon

10 Comments

Stephen Last Over a year ago

Thanks Sam, that obviously works, however I was looking for a different way (other than traversing the whole array). I guess count($myarray, COUNT_RECURSIVE_NUMERIC); would be perfect, but doesn't exist.

anon Over a year ago

@CrusaderLtd, as far as I know, there (as you say), isn't a way to do this in PHP by default, so a custom wrapper which iterates through the array is the best way (I'm sure PHP would do the same thing)

anon Over a year ago

@CrusaderLtd, the other way would be to use array_keys and loop through that, but that again is not recursive through all the parts (AFAIK), see the test at the bottom of my answer

anon Over a year ago

@CrusaderLtd, may I ask why you do not want to iterate through the whole array? (Seems like a bad idea because without traversal/iteration you are not going to get all the arrays that are nested counted)

Stephen Last Over a year ago

@SamSwift웃 Of course, you took the recursion out, I'll use a recursive function with ternary operators. :-)

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