PHP loop according to amount of items in array

Question

I'm trying to write a short script that will query my mysql db, and according to the amount of results (dynamic) i want the script on each segment.

For example, $arr is a result of a mysql_fetch_array and it has 872 items, I want to run my function 9 times, 1 for each 100 items and the last one for 72 items.

How can I do that?

Do you want each segment you loop over to be a maximum of 100 items? — vascowhite
– vascowhite, Commented Jun 25, 2011 at 17:07

Andrew Moore · Accepted Answer · 2011-06-25 17:13:01Z

3

Simply use a for loop with an incrementor that increments by 100. You can use array_slice() to get the concerned rows on each loop.

$dbRows = resultsFromDB();

for($i = 0; $i < count($dbRows); $i+=100) {
  $concernedRows = array_slice($dbRows, $i, 100);

  mySuperFunction($concernedRows);
}

answered Jun 25, 2011 at 17:13

Andrew Moore

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4 Comments

Ondřej Mirtes Over a year ago

Placing count() function in for condition slows down the execution, because it counts the items every loop pass.

Andrew Moore Over a year ago

@Ondřej Mirtes: No it doesn't. count() doesn't loop through the elements to count, it simply accesses a property of the zend_hash. I invite you to browse around the PHP source; specifically at zend_hash_num_elements() and PHP_FUNCTION(count). The number of items in an PHP Array (Zend Hash) is automatically updated on insertion/deletion. An array with 1,000,000 elements takes as long as an empty array to count.

Ondřej Mirtes Over a year ago

I was talking about this: codeforest.net/php-mythbusters-count-inside-for-loop-is-slow

Andrew Moore Over a year ago

@Ondřej Mirtes: He's wrong. Try it out yourself and check the PHP source. Any contributor will tell you that the only overhead of calling count() versus storing the result in a variable is the function call. That's it. O(1).

Doug Owings · Accepted Answer · 2011-06-25 17:07:23Z

2

Maybe something like:

$length = count($arr);

for ($i = 0; $i < ceil($length / 100); $i++) {

}

If I understood.

answered Jun 25, 2011 at 17:07

Doug Owings

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3 Comments

Or Weinberger Over a year ago

For some reason, the loop runs only 108 times ($i = 108 after the loop ends) and count($arr) = 2700

Andrew Moore Over a year ago

@Or W: "only"? By your specification, an array of 2700 items should only run your function 27 times, not 108 times.

Doug Owings Over a year ago

@Or W, maybe show the rest of the code you implemented it in. Try running $length = 2700; echo ceil($length / 100);. Should output 27

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