Re^7: Write code diferently (A little knowledge is a dangerous thing.)

Your benchmark, on which you base all your demonstration that I am wrong and that you are right, is just hot air and pure baloney. And it is plain wrong.

Wrong! All you've done is show how little you understand about Perl.

You didn't replicate my benchmark correctly. I posted this:
```
cmpthese -3,{a=>q[@a = map $_*1, @a],b=>q[map $_*=1, @a],c=>q[$_*=1 fo
+r @a] };;
[download]
```
You used this:
```
timethese (10000000,{a=>q{map {1} @a},b=>q[map $_*=1, @a],c=>q[$_*=1 f
+or @a] });
[download]
```
Spot your idiocies:.
1. a=>q{map {1} @a}
  Where did your get that from? Cos it wasn't my benchmark.
2. Now the biggy: my @a = 1..1000000;.
  How d'you expect code that is eval'd from a string, to see a lexical array?
  Since you seem incapable of understanding stuff that requires a little knowledge; try downloading this and running it on your laptop(and post the results if you dare!):
  <Reveal this spoiler or all in this thread>

Multiplying a value by 1 is not terribly useful, and part of your code is probably optimized away.

Again, you show your lack of knowledge. Multiplying by one does not get optimised away.

Now, let's do a real benchmark:

You're joking right? Because your benchmark is crap.

You are timing how long it takes:

to allocate an array;
and then populate it;
and the time taken to call a subroutine (the one you wrote) from within a subroutine (the one Benchmark wraps around the code ref (or string) you give to it.)
in addition to the time taken to iterate it..

Let's start with your benchmark as posted (minus the eclectic formatting), run on my machine:

timethese 10000, {
    "idiomatic" => sub { my @array = 1..1000;      $_ +=2 for @array; 
+},
    "map"       => sub { my @array = 1..1000; map{ $_ +=2;}   @array; 
+},
};

__END__
C:\test>IdiotsBench.pl
Benchmark: timing 10000 iterations of idiomatic, map...
 idiomatic:  2 wallclock secs ( 1.52 usr +  0.00 sys =  1.52 CPU) @ 65
+96.31/s (n=10000)
       map:  3 wallclock secs ( 3.06 usr +  0.00 sys =  3.06 CPU) @ 32
+64.77/s (n=10000)
[download]

Now let's remove those array allocations and populations from the timing:

C:\test>IdiotsBench.pl
my @array = 1..1000;
timethese 10000, {
    "idiomatic" => sub {      $_ +=2 for @array; },
    "map"       => sub { map{ $_ +=2 }   @array; },
};

__END__
C:\test>IdiotsBench.pl
Benchmark: timing 10000 iterations of idiomatic, map...
 idiomatic:  1 wallclock secs ( 0.92 usr +  0.00 sys =  0.92 CPU) @ 10
+845.99/s (n=10000)
       map:  2 wallclock secs ( 2.44 usr +  0.00 sys =  2.44 CPU) @ 41
+01.72/s (n=10000)
[download]

Now let's remove the expensive and redundant block scope from the map test:

C:\test>IdiotsBench.pl
timethese 10000, {
    "idiomatic" => sub {     $_ +=2 for @array; },
    "map"       => sub { map $_ +=2,    @array; },
};

__END__
Benchmark: timing 10000 iterations of idiomatic, map...
 idiomatic:  1 wallclock secs ( 0.95 usr +  0.00 sys =  0.95 CPU) @ 10
+493.18/s (n=10000)
       map:  1 wallclock secs ( 0.95 usr +  0.00 sys =  0.95 CPU) @ 10
+493.18/s (n=10000)
[download]

And finally, the double function call:

our @array2 = 1 .. 1000;
timethese 10000, {
    "idiomatic" => q[     $_ +=2 for @array2; ],
    "map"       => q[ map $_ +=2,    @array2; ],
};

__END__
Benchmark: timing 10000 iterations of idiomatic, map...
 idiomatic:  1 wallclock secs ( 0.88 usr +  0.00 sys =  0.88 CPU) @ 11
+428.57/s (n=10000)
       map:  1 wallclock secs ( 0.84 usr +  0.00 sys =  0.84 CPU) @ 11
+848.34/s (n=10000)
[download]

And waddayaknow; now we are benchmarking just the disputed code and not conflating it with a bunch other random stuff, map is faster than for. Just like I said.

You want to withdraw your accusation of phony results now?

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

Comment on Re^7: Write code diferently (A little knowledge is a dangerous thing.) Select or Download Code

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Re^8: Write code diferently (A little knowledge is a dangerous thing.) by Laurent_R (Canon) on Aug 29, 2013 at 00:18 UTC
Alright, I must apologize, I made an error while trying to use your benchmark. I am sorry about that and about what I said about your tests. try downloading this and running it on your laptop(and post the results if you dare!) No need to be very daring, I can recognize a mistake of mine when that occurs. I admit that I was wrong on this point. How d'you expect code that is eval'd from a string, to see a lexical array? Of course, code that is eval'd from a string can see a lexical array. Just an example: `use strict; use warnings; my $c = "foo"; my $d = "print q{$c}, q{\n}"; eval ($d); # print "foo" my @f = 1..10; process_f(); sub process_f { my $g = 'print "$_ " for @f; print "\n";'; eval ($g); } my $h = 'my $i = sub { print map {$_ = 2; "$_ ";} @f; print "\n" }; $ +i->();'; eval ($h);` [download] Here, the problem occurs only because the string is passed to a module function in a separate file, so that the lexical is neither passed as an argument, nor seen as a global. Which is by the way the reason why I don't like using the string version for the Benchmark module and almost never use it. And this is why I made the silly mistake, almost never using this form. map is faster than for. Just like I said.* I don't think this is true. I've tried your code a dozen times on three different version of Perl, for was almost always faster than map by a very thin margin. As a final test, I increased the number of iterations to 50,000 on Perl 5.18/Windows 7: `use strict; use warnings; use Benchmark; our @array2 = 1 .. 1000; timethese 50000, { "idiomatic" => q[ $_ +=2 for @array2; ], "map" => q[ map $_ +=2, @array2; ], };` [download] Results for 5 runs: Benchmark: timing 50000 iterations of idiomatic, map... idiomatic: 3 wallclock secs ( 2.87 usr + 0.00 sys = 2.87 CPU) @ 17 +421.60/s ( n=50000) map: 3 wallclock secs ( 3.04 usr + 0.00 sys = 3.04 CPU) @ 16 +436.55/s ( n=50000) Benchmark: timing 50000 iterations of idiomatic, map... idiomatic: 3 wallclock secs ( 2.87 usr + 0.00 sys = 2.87 CPU) @ 17 +421.60/s ( n=50000) map: 3 wallclock secs ( 3.04 usr + 0.00 sys = 3.04 CPU) @ 16 +436.55/s ( n=50000) Benchmark: timing 50000 iterations of idiomatic, map... idiomatic: 3 wallclock secs ( 2.86 usr + 0.00 sys = 2.86 CPU) @ 17 +513.13/s ( n=50000) map: 3 wallclock secs ( 3.04 usr + 0.00 sys = 3.04 CPU) @ 16 +436.55/s ( n=50000) Benchmark: timing 50000 iterations of idiomatic, map... idiomatic: 3 wallclock secs ( 2.87 usr + 0.00 sys = 2.87 CPU) @ 17 +415.53/s ( n=50000) map: 3 wallclock secs ( 3.04 usr + 0.00 sys = 3.04 CPU) @ 16 +436.55/s ( n=50000) Benchmark: timing 50000 iterations of idiomatic, map... idiomatic: 3 wallclock secs ( 2.87 usr + 0.00 sys = 2.87 CPU) @ 17 +421.60/s ( n=50000) map: 3 wallclock secs ( 3.04 usr + 0.00 sys = 3.04 CPU) @ 16 +436.55/s ( n=50000) [download] The results are very consistent throughout and it certainly cannot be said that map is faster than for. At best, they are more or less equivalent. But my initial point has never been about performance anyway, but only to suggest a possible explanation for the OP's original question. Again, I did not want to have a debate with you on this subject in the first place, because I think we were agreeing on most things. And I want to reiterate that I am sorry that I made an error leading me to believe and to say wrongly that your test was wrong.	[reply] [d/l] [select]
Re^9: Write code diferently (A little knowledge is a dangerous thing.) by BrowserUk (Patriarch) on Aug 29, 2013 at 00:49 UTC
I am sorry that I made an error Thank you, and respect. Here are 3 runs each of 5.10.1 (my default installation) and 5.18.0 (self-compiled with MSVC VS v9.0) both running under Vista + SP1 on my hardware: C:\test>IdiotsBench.pl Rate idiomatic-my-sub map-my-scope-sub idiomatic-my-sub 10817/s -- -7% map-my-scope-sub 11597/s 7% -- C:\test>IdiotsBench.pl Rate idiomatic-my-sub map-my-scope-sub idiomatic-my-sub 11113/s -- -8% map-my-scope-sub 12126/s 9% -- C:\test>IdiotsBench.pl Rate idiomatic-my-sub map-my-scope-sub idiomatic-my-sub 10760/s -- -11% map-my-scope-sub 12126/s 13% -- C:\test>\perl5.18\bin\perl.exe IdiotsBench.pl Rate map-my-scope-sub idiomatic-my-sub map-my-scope-sub 10426/s -- -9% idiomatic-my-sub 11438/s 10% -- C:\test>\perl5.18\bin\perl.exe IdiotsBench.pl Rate map-my-scope-sub idiomatic-my-sub map-my-scope-sub 10455/s -- -7% idiomatic-my-sub 11269/s 8% -- C:\test>\perl5.18\bin\perl.exe IdiotsBench.pl Rate map-my-scope-sub idiomatic-my-sub map-my-scope-sub 10521/s -- -7% idiomatic-my-sub 11263/s 7% -- [download] So yes, the balance of power has shifted slightly. my initial point has never been about performance anyway, but only to suggest a possible explanation for the OP's original question. Which I understood to be so. But, there is no logical reason for denigrating the use of map in a void context. Your argument for clarity -- an argument that is very close to my heart -- is false also; because it relies upon the assumption, or presumption, that map must return a list; rather than just 'applies a function to a list'. You are (relatively) new around here; and I urge you to read and digest the writings of Abigail/Abigail-II, there is little that s/he said on the subject of Perl that isn't worthy if serious note. With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday' Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error. "Science is about questioning the status quo. Questioning authority". In the absence of evidence, opinion is indistinguishable from prejudice.	[reply] [d/l]