Re: Alternative of Push operation

From where "do we know" that the push operation is costly? Compared with what? Because it's a perl build-in it's already highly optimized C code so I don't think that any Perl code can be more efficient.
If you look in perldoc -f push:

[push @ARRAY, LIST] Has the same effect as
   for $value (LIST) {
      $ARRAY[++$#ARRAY] = $value;
   }
but is more efficient.
[download]

IMHO the best way to make your code more efficient, i.e. less-costly, is to recode you script so it's doesn't need a push operation any more.

The most expensive thing with push might be the (re-)allocation of new memory, so if you would initialize the array with the final size at the start, e.g. $#array = 1000;, and use splice instead of push then you might save time. Please post a compare benchmark here if you code that.

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Re^2: Alternative of Push operation by mscharrer (Hermit) on Apr 28, 2008 at 12:35 UTC
I was curious so I wrote a benchmark for this. (Please note that benchmarks must be interpreted correctly and are sometimes not very meaningful, see 588703.) Read more... (1026 Bytes) The results are very interesting: `Rate for splice splice2 push for 484262/s -- -59% -67% -76% splice 1169591/s 142% -- -21% -42% splice2 1481481/s 206% 27% -- -27% push 2020202/s 317% 73% 36% --` [download] As awaited the `for` loop is the slowest way to do it. `push` is the fastest of all. Using `splice` is quite in between of both. The interesting and surprising thing is that splice is faster without pre-allocating the array ('splice2') then with ('splice'). The moral of this seems to be: Perl build-ins are already very optimized - don't try to replace them with your own Perl code. If you need something done which is covered by a build-in function - use it. And don't think about it. If you need more performance you are using the wrong programming language!	[reply] [d/l] [select]

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Re^2: Alternative of Push operation
by mscharrer (Hermit) on Apr 28, 2008 at 12:35 UTC

588703

Read more... (1026 Bytes)

             Rate     for  splice splice2    push
for      484262/s      --    -59%    -67%    -76%
splice  1169591/s    142%      --    -21%    -42%
splice2 1481481/s    206%     27%      --    -27%
push    2020202/s    317%     73%     36%      --
[download]

for

push

splice

is faster without pre-allocating

The moral of this seems to be:
Perl build-ins are already very optimized - don't try to replace them with your own Perl code.
If you need something done which is covered by a build-in function - use it. And don't think about it. If you need more performance you are using the wrong programming language!

[reply]
[d/l]
[select]