sub first (&@) {
  my $cref = shift;
  $cref->($_) and return $_ for @_;
}
[download]

# get the first number found over 1000
$first_match = first { $_ > 1000 } @numbers;
[download]

my %seen;
@seen{@array} = ();
[download]

if (exists $seen{blah}) { ... }
[download]

One thousand pardons, m'lord japhy, but you wrote:

But if you do this a lot of times, you're kissing inefficiency on its ratty lips. Use a hash:

In the oft-maligned name of pragmatism, I cobbled together the following brief, unscientific test:

#!/usr/bin/perl -w

use Benchmark;

@List = ("aaaa" .. "zzzz");
print "Elements:", scalar @List, "\n";

sub first (&@) {
  my $cref = shift;
  $cref->($_) and return $_ for @_;
}

$t0 = new Benchmark;
$first_match = first {$_ eq "zzzz"} @List;
$t1 = new Benchmark;
$td = timediff($t1, $t0);

print "Found it! (sub)\n" if $first_match;
print "sub took: ", timestr($td), "\n";

# Crufty way to figure out how big I am on a Linux box - /msg me with 
+improvements, please! -McD
$size = (split(" ", `ps -hlp $$`))[6];
print "Size: $size\n";


$t0 = new Benchmark;
my $Found=0;
for (@List) {
  if ($_ eq "zzzz") {
    $Found=1;
    last;
  }
}
$t1 = new Benchmark;
$td = timediff($t1, $t0);

print "Found it! (scan)\n" if $Found;
print "scan took: ", timestr($td), "\n";
$size = (split(" ", `ps -hlp $$`))[6];
print "Size: $size\n";



$t0 = new Benchmark;
my %seen;
@seen{@List} = ();
$t1 = new Benchmark;
$td = timediff($t1, $t0);

if (exists $seen{"zzzz"}) { print "Found it! (hash)\n"; }
print "hash took: ", timestr($td), "\n";
$size = (split(" ", `ps -hlp $$`))[6];
print "Size: $size\n";
[download]

To make this a worst-case for the linear teams, I searched for the last item in the list.

As it turns out, the least appealing code is the fastest - but while the hash approach may not be kissing performance inefficiency on it's ratty lips, it's certainly been caught in some kind of carnal embrace with memory inefficiency.

Here are the results on my box:

./existance.pl
Elements:456976
Found it! (sub)
sub took:  2 wallclock secs ( 1.49 usr +  0.01 sys =  1.50 CPU)
Size: 58632
Found it! (scan)
scan took:  1 wallclock secs ( 0.40 usr +  0.00 sys =  0.40 CPU)
Size: 58632
Found it! (hash)
hash took:  2 wallclock secs ( 0.90 usr +  0.15 sys =  1.05 CPU)
Size: 88324

Of course, we've strayed far from meditation and into experimentation. I'm sorry, what were we optimizing for again? :-)

Peace,
-McD

You quoted me, and then didn't follow my lead. "But if you do this a lot of times, you're kissing inefficiency on its ratty lips."

You performed these tests ONCE each. Use the first() function several times. Scan through the array several times. Create the hash ONCE, and use exists() many times.

japhy -- Perl and Regex Hacker

Here's my test. first() can be made faster by passing an array reference, not the array.

(RESULTS)
Elements:17576
sub took:  52 (51.14 usr +  0.00 sys = 51.14 CPU)
scan took: 17 (13.85 usr +  0.00 sys = 13.85 CPU)
hash took:  0 ( 0.17 usr +  0.13 sys =  0.30 CPU)

(CODE)
#!/usr/bin/perl -w

use Benchmark;

@List = ("aaa" .. "zzz");
print "Elements:", scalar @List, "\n";

@rand_list = map $List[rand @List], 1 .. 100;

sub first (&@) {
  my $cref = shift;
  $cref->($_) and return $_ for @_;
}

$t0 = new Benchmark;
for (@rand_list) {
  $rand_element = $_;
  $first_match = first {$_ eq $rand_element } @List;
}
$t1 = new Benchmark;
$td = timediff($t1, $t0);
print "sub took: ", timestr($td), "\n";


$t0 = new Benchmark;
for (@rand_list) {
  $rand_element = $_;
  for (@List) { last if $_ eq $rand_element }
}
$t1 = new Benchmark;
$td = timediff($t1, $t0);
print "scan took: ", timestr($td), "\n";



$t0 = new Benchmark;
my %seen;
@seen{@List} = ();
$t1 = new Benchmark;
$td = timediff($t1, $t0);
for (@rand_list) { 1 if exists $seen{$_} }
print "hash took: ", timestr($td), "\n";
[download]



japhy -- Perl and Regex Hacker

;)))

As you might have read, I would have used a hash....

I was trying to find an example of beauty/efficiency
sad enough, that was the best I could come up with ;))

I would have probably used 'eq' instead of the regex too ;)))

GreetZ!,

ChOas

print "profeth still\n" if /bird|devil/;

Well, an interesting feature of Perl is that by using its data structures, one can often make a structure representing some complex algorithm (like a hash being used to eliminate duplicates).

japhy -- Perl and Regex Hacker

If I were implementing such a "have I got that item in my list?" function, I would also include in the code the "key" to where in the list that item is, just in case I will want to do something to that item. Now, if we use a hash, then we get that:

$my_hash{$key_value} = 'Stuff up the value real good';
[download]

If it wasn't first thing in the morning, I would attempt to hack a bit of code demonstrating this, but I am sure you all know what I mean here. The essence of what I am saying is that a good programmer looks ahead, and allows for the foreseeable future requirements.

Updated: Stupid typo in code fragment fixed. I should finish my coffee before coding.