So I was curious about the performance of some of the methods mentioned in the answers for large number of integers.

Preparation

Just creating an array of 1 million random integers between 0 and 100. Than, I imploded them to get the string.

  $integers = array();
  
  for (i < 1000000; $i++) {
      $integers[] = rand(0, 100);
  }

  $long_string = implode(',', $integers);

Method 1

This is the one liner from Mark's answer:

$integerIDs = array_map('intval', explode(',', $long_string));

Method 2

This is the JSON approach:

  $integerIDs = json_decode('[' . $long_string . ']', true);

Method 3

I came up with this one as modification of Mark's answer. This is still using explode() function, but instead of calling array_map() I'm using regular foreach loop to do the work to avoid the overhead array_map() might have. I am also parsing with (int) vs intval(), but I tried both, and there is not much difference in terms of performance.

  $result_array = array();
  $strings_array = explode(',', $long_string);
  
  foreach ($strings_array as $each_number) {
      $result_array[] = (int) $each_number;
  }

Results

Method 1        Method 2        Method 3
0.4804770947    0.3608930111    0.3387751579
0.4748001099    0.363986969     0.3762528896
0.4625790119    0.3645150661    0.3335959911
0.5065748692    0.3570590019    0.3365750313
0.4803431034    0.4135499001    0.3330330849
0.4510772228    0.4421861172    0.341176033
0.503674984     0.3612480164    0.3561749458
0.5598649979    0.352314949     0.3766179085
0.4573421478    0.3527538776    0.3473439217
        
0.4863037268    0.3742785454    0.3488383293

The bottom line is the average. It looks like the first method was a little slower for 1 million integers, but I didn't notice 3x performance gain of Method 2 as stated in the answer. It turned out foreach loop was the quickest one in my case. I've done the benchmarking with Xdebug.

Edit: It's been a while since the answer was originally posted. To clarify, the benchmark was done in php 5.6.40.

So Ed-Heal already sent a really good answer, and more efficient, but I will post one with a for loop just to explain the process:

$stringArray = array("2","5"); // We set up the string array

var_dump($stringArray);

// We loop through the array:
for ($i = 0; $i<sizeof($stringArray); $i++) {
    // We set the value at the index $i to an integer.
    $stringArray[$i] = intval($stringArray[$i]);
}

var_dump($stringArray);

The output of the code above would be as follows

array(2) { [0]=> string(1) "2" [1]=> string(1) "5" }
array(2) { [0]=> int(2) [1]=> int(5) } 

So what does this code do? Well we loop through the array, we grab every value and change it with a integer with the function intval().

Oh and please, don't capsize your question's title.

You can use array_map

$TaxIds = array_map(function($value) {
    return intval($value);
}, $TaxIds);

intval() does not set the value, it only returns the value.

You could do this:

array_walk($numArray, function(&$x){$x = intval($x);});

return array_map('intval', explode(",", '1,2,3,4,5,6,7,8,9'));

use str_split() function

$array = str_split($str);

http://php.net/manual/en/function.str-split.php