Undefined offset with count()

Question

I have an array $MyArray which has some elements which are also array (lets call them subarrays). I want to know how many elements the subarray with the most elements has. The problem is, that I don't know if the index exists:

 max(
     @count($MyArray[$i*7]), 
     @count($MyArray[$i*7+1]), 
     @count($MyArray[$i*7+2]),         
     @count($MyArray[$i*7+3]),
     @count($MyArray[$i*7+4]),
     @count($MyArray[$i*7+5]),
     @count($MyArray[$i*7+6])
 );

Struckture of $MyArray:

Array(
  12 => array ( 
        0 => array ( 0 => 0, 1 => 1, ), 
        1 => array ( 0 => 13, 1 => 1, ), 
        2 => array ( 0 => 15, 1 => 1, ), 
        3 => array ( 0 => 20, 1 => 1, ), 
        4 => array ( 0 => 69, 1 => 1, ) 
  ),
  5 => array ( 
        0 => array ( 0 => 55, 1 => 1, ), 
        1 => array ( 0 => 32, 1 => 1, ), 
        2 => array ( 0 => 12, 1 => 1, ), 
        3 => array ( 0 => 21, 1 => 5, ) 
  ),
  ....
)

Can this be done better (faster)?

edit: I know foreach and I don't want to loop over every element in this array. I just want an interval of it. @ is used, because I don't know if $MyArray[$i*7 + x] is Null or an array.

$i is a element of [0, 1, 2, 3, 4] (sometimes also 5)

so, basically you have one array with many subarrays, and the goal is to get the subarray with the highest number of element and count it's total elements? — KJYe.Name, Jan 19 '11 at 17:41
@kjy112, goal is to just count that subarray's elements, not even get that subarray. — shamittomar, Jan 19 '11 at 17:45
I don't get how most the answers use `foreach` and completely ignore the `$i*7+y` bit, especially since `$MyArray` structure is unknown... — netcoder, Jan 19 '11 at 17:57
@netcoder: I upvoted your answer for doing that, but I don't feel the question is fully clear yet. — Jonah, Jan 19 '11 at 18:13

Jonah · Answer 1 · 2011-01-19T17:46:05.347

4

$biggest = 0;
foreach ($MyArray as $value) {
    if ($biggest < count($value)) {
        $biggest = count($value);
    }
}

I see, you want the size of the biggest array in the array, correct?

edited Jan 19 '11 at 17:46

answered Jan 19 '11 at 17:39

Jonah

9,991
5
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I'd upvote you, but you are unnecessarily calling `count` twice – brian_d Jan 19 '11 at 17:48
1

@brain_d: I'm pretty sure that's not a concern. `count()` just gets the size, it doesn't actually _count_ them. And storing it into an array just creates a variable, which uses up processing. Plus, caching is not necessary to convey the concept. Thanks for the observation though. – Jonah Jan 19 '11 at 17:51
2

+1 I was not aware it was O(1). http://stackoverflow.com/questions/4566314/php-what-is-the-complexity-i-e-o1-on-of-the-function-count – brian_d Jan 19 '11 at 18:25

score 3 · Answer 2 · answered Jan 19 '11 at 17:42

Simple and old school approach:

<?php

$max = -1;
foreach($MyArray as $subarray)
{
    $items = count($subarray);
    if($items > $max)
         $max = $items;
}

echo $max;
?>

This works best since you only want to know how many elements the subarray with the most elements has.

score 3 · Answer 3 · answered Jan 19 '11 at 17:49

3

$max = 0;
foreach ($MyArray as $value) {
    $max = max($max,count($value));
}

answered Jan 19 '11 at 17:49

Mark Baker

209,507
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1

`$max = $MyArray ? max(array_map('count', $MyArray)) : 0;` is even better IMO :-) – Arnaud Le Blanc Jan 21 '11 at 09:27
@user576875: 8O that's awesome. I didn't know you could pass an array to `max`. – Jonah Aug 14 '11 at 22:06

score 2 · Accepted Answer · answered Jan 19 '11 at 17:42

2

Try this:

$arr = array();
for ($j=0;$j<=6;$j++) {
   if (isset($MyArray[$i*7+$j])) $arr[] = count($MyArray[$i*7+$j]);
}
$result = max($arr);

I don't know exactly what $i refers to though...

answered Jan 19 '11 at 17:42

netcoder

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Hi netcoder, thanks for your script. It seems like it is the fastest (see http://martin-thoma.blogspot.com/2011/01/benchmarking-php.html). I thought using more functions (`isset` + `count`) would take more time than simply surpressing the warnings with `@` and don't using `isset`. – Martin Thoma Jan 21 '11 at 07:10

Arnaud Le Blanc · Answer 5 · 2011-01-22T12:40:17.030

1

// get the interesting part of the array
$chunk = array_intersect_key($input_array, array_flip(range($i*7, $i*7+6))); 
// max(count)
$max = $chunk ? max(array_map('count', $chunk)) : 0;

edited Jan 22 '11 at 12:40

answered Jan 19 '11 at 17:57

Arnaud Le Blanc

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Well, this wasn't exactly right, but almost. range gives values, but I need keys: $chunk = array_intersect_key($MyArray, array($i*7=>1, $i*7+1=>2, $i*7+2=>3, $i*7+3=>4, $i*7+4=>5, $i*7+5=>6)); if(count($chunk) > 0){$max = max(array_map('count', $chunk));} else {$max = 0;} – Martin Thoma Jan 21 '11 at 05:54
ah you are right; then `$chunk = array_intersect_key($input_array, array_flip(range($i*7, $i*7+6))); $max = $chunk ? max(array_map('count', $chunk)) : 0;` – Arnaud Le Blanc Jan 21 '11 at 09:16

Undefined offset with count()

5 Answers5