I'm iterating over a huge array and it involves querying multiple APIs so to avoid data loss and timeout, I'm doing this:
for ($i = 0; $i < $count; $i++) {
if ($i % 100 == 0) {
echo 'processed: '.$i."\n";
// save to file
}
}
... it works if the loop is a few hundred iterations during test and outputs processed ..., but nothing at all in prod environment during the script is running, it echos everything only after its done. I just want to avoid any timeouts incase it takes (and usually does) long.
PHP output is buffered; see here. If you flush the buffer (or turn buffering off), you'll see it happen in real-time.
As "belt and braces", if you really care about the output, I'd echo the $count before you even enter the loop.
what is the aim of this code block?
well, until $i reaches 100, it is waste of resource anyway..
you can try:
if( $count > 100 ) {
ini_set('max_execution_time', 0); // no time limit
// $count contains at least $i times 100
for($i = 1; $i <= $count / 100; $i++) {
echo $i * 100;
}
}
Related
I'm somewhat new to PHP, been reading a few books and I've never seen a loop where it gets you all the even numbers(for example from 1 to 10), so I decided to try it myself:
for($i=0;$i<10 && $i % 2===0;$i++)
echo $i;
Tried with only double == as well.
And this,
$i=0;
do echo $i; while($i++<10 && $i % 2 ==0);
Can't seem to figure out how to use 2 conditions in the same statement.
Would appreciate the help!
Thanks.
Try to use this code
for( $i=0; $i<=10; $i++ )
{
if( $i%2 == 0 ){
echo $i;
}
}
The loop is breaking entirely when the second condition fails the first time. On the first iteration: 0 is less than 10, and it is even, so the loop iterates. On the second iteration: 1 is less than 10, but is odd, so the loop breaks.
Your code is the equivalent of this:
for($i=0; $i<10; $i++) {
if ($i % 2 !==0 ) {
break;
}
echo $i;
}
0
You can eliminate the second condition of your for loop to prevent the breakage and rely exclusive on a third expression to increment $i by two each iteration.
for($i=0; $i<10; $i = $i + 2) {
echo $i;
}
02468
The second statement in a for-loop is/are the condition(s) which gets checked every loop. so if it fails your loop stops. what you need will look somewhat like this:
for ($i = 0; $i < 10; $i++)
if ($i % 2 == 0)
echo $i;
So the loop will run over every number but only print out the even ones.
You don't need to loop.
Range can create a range with third parameter step 2.
$arr = range(0,20,2);
Echo implode(" ", $arr);
https://3v4l.org/S3JWV
you can use also regular loop and get the evens by formula:
for($i=0; $i<10 ;$i++) {
$j = $i * 2;
// do somthing with $j witch loop over 10 first evens...
}
Im trying to slice an array on 30 at a time to send a call to an endpoint which can only recibe 30 codes at a time. Right now I have about 203 lines in the array. Everything is fine until the 4th round where I don't know why the indexes (init and endt) I've set up, get messed up and the slice no longer works which in turns makes the call to the endpoint impossible. Here is the code:
$arrcount = ceil(count($requestarr['SelectionDetails'])/30);
$init = 0;
if (count($requestarr['SelectionDetails']) > 30) {
$endt = 29;
} else {
$endt = count($requestarr['SelectionDetails']);
}
for ($i=0; $i < $arrcount; $i++) {
$request['SelectionDetails'] = array_slice($requestarr['SelectionDetails'], $init, $endt);
$init = $endt+1;
if (count($requestarr['SelectionDetails']) > ($endt+30)) {
$endt += 30;
} else {
$endt = count($requestarr['SelectionDetails']);
}
//call to endpoind and other code here....
}
The requestarr[] has the whole 203 indexes and the request[] contains the 30 indexes slice sent each loop. Its worth noticing that my array has "custom" keys that are tracking numbers from FedEx. At the 4th loop, the init turns into 120 and the endt turns into 113. Im not sure how or why this happens. Needless to say the next 3 for loops the endt gets reduced by 7 then by 34 and finally by 1. There is no code where the endt should be decreasing. So I'm not sure how this is happening. Any ideas? If you need more information or more code I'll gladly help.
To split items into chunks - use array_chunk:
$chunks = array_chunk($your_data, 30);
foreach ($chunks as $chunk) {
// send $chunk to endpoint
}
$arrcount = ceil(count($requestarr['SelectionDetails'])/30);
for ($i=0; $i < $arrcount; $i++) {
$request['SelectionDetails'] = array_slice($requestarr['SelectionDetails'], $i * 30, 30);
//call to endpoind and other code here....
}
array_slice can take a length argument longer than the array. You just have to move the starting point.
I have a for loop in my code. I haven't changed anything on this part of code for about 5-6 days and I never had problems with it.
Since yesterday I tried to reload my code and it allways gives me this error:
Maximum execution time of 30 seconds exceeded - in LogController.php line 270
Well I can't explain why but maybe someone of you could look over it.
This is my code around line 270.
$topten_sites = [];
for ($i = 0; $i <= count($sites_array); $i++) {
if ($i < 10) { // this is 270
$topten_sites[] = $sites_array[$i];
}
}
$topten_sites = collect($topten_sites)->sortByDesc('number')->all();
As I said, it worked perfectly, so why it gives me an error? If I uncomment these lines and every other line that contains the $topten_sites array, the code workes again.
This looks wrong:
for ($i = 0; $i <= $sites_array; $i++) {
if ($i < 10) { // this is 270
$topten_sites[] = $sites_array[$i];
}
}
If $sites_array is an array, it makes no sense to compare it to an integer so you probably have a never-ending loop.
If you just need the first 10 elements in another array, you can replace your loop with:
$topten_sites = array_slice($sites_array, 0, 10);
Why would You iterate entire array if You only want first 10 results?
for ($i = 0; $i < 10; $i++) {
$topten_sites[] = $sites_array[$i];
}
To answer the actual answer; code never stops working "for no reason". Code works or it doesn't, both for a reason. If it stops working something changed compared to your previous tests.
"Sometimes it works, sometimes it doesn't" falls in the same logic. Code will always behave exactly the same every time, just some of the parameters have changed, you have to find which one.
In your case, i'm guessing the entries in your array have increased. PHP and arrays aren't best friends when it comes to speed, arrays are slow. It could very well be that your array was
smaller when you tested it (wasn't probally the fastest to begin with), but now with the current amount it just hit the threshold of 30 seconds.
It could also be that a part of code before this bit of code takes a lot of time (say suddenly 28 seconds instead of 20), and your loop (which never changed) does it's job in the regular 3seconds it always does, now runs into problems
Use it like this:
$topten_sites = [];
for ($i = 0; $i <= 10; $i++) {
$topten_sites[] = $sites_array[$i];
}
$topten_sites = collect($topten_sites)->sortByDesc('number')->all();
I know the more efficient way to have a loop over array is a foreach, or to store count in a variable to avoid to call it multiple times.
But I am curious if PHP have some kind of "caching" stuff like:
for ($i=0; $i<count($myarray); $i++) { /* ... */ }
Does it have something similar and I am missing it, or it does not have anything and you should code:
$count=count($myarray);
for ($i=0; $i<$count; $i++) { /* ... */ }
PHP does exactly what you tell it to. The length of the array may change inside the loop, so it may be on purpose that you're calling count on each iteration. PHP doesn't try to infer what you mean here, and neither should it. Therefore the standard way to do this is:
for ($i = 0, $length = count($myarray); $i < $length; $i++)
PHP will execute the count each time the loop iterates. However, PHP does keep internal track of the array's size, so count is a relatively cheap operation. It's not as if PHP is literally counting each element in the array. But it's still not free.
Using a very simple 10 million item array doing a simple variable increment, I get 2.5 seconds for the in-loop count version, and 0.9 seconds for the count-before-loop. A fairly large difference, but not 'massive'.
edit: the code:
$x = range(1, 10000000);
$z = 0;
$start = microtime(true);
for ($i = 0; $i < count($x); $i++) {
$z++;
}
$end = microtime(true); // $end - $start = 2.5047581195831
Switching to do
$count = count($x);
for ($i = 0; $i < $count; $i++) {
and otherwise everything else the same, the time is 0.96466398239136
PHP is an imperative language, and that means it is not supposed to optimize away anything that can possibly have any effect. Given that it's also an interpreted language, it couldn't be done safely even if someone really wanted.
Plus, if you simply want to iterate over the array, you really want to use foreach. In that case, not only the count, but the whole array will be copied (and you can modify the original one as you wish). Or you can modify it in place using foreach ($arr as &$el) { $el = ... }; unset($el);. What I mean to say is that PHP (as any other language) often provides better solutions to your original problem (if you have any).
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?
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);
}
Maybe something like:
$length = count($arr);
for ($i = 0; $i < ceil($length / 100); $i++) {
}
If I understood.