convert each character of a string to number

Lowry76 has asked for the wisdom of the Perl Monks concerning the following question:

Hi all I'm looking for a fast way of converting a sequence of four characters (a,b,c,d) to a number. So far I use

my $lt = [];
$lt->[ord(a)] = 00;
$lt->[ord(b)] = 01;
$lt->[ord(c)] = 10;
$lt->[ord(d)] = 11;

foreach my $string{
_convert($string);

...
sub _convert{
my $string = shift;
my $bs="";
foreach(split(//,$string)){

$bs.=$lt->[$_];
}

return int($bs);
}
[download]

I also tried using a hash of form {a=>00,b=>01,c=>10,d=>11} or use four substitutes on $string which should have been kind of four times the runtime (processing the complete string 4 times). But somehow the regexp substitution seems to be the fastest. However, it's still pretty slow if I'm iterating over millions of strings. Any faster solution? Cheers, Lowry

Comment on convert each character of a string to number Download Code

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Re: convert each character of a string to number by tybalt89 (Monsignor) on Feb 12, 2017 at 04:04 UTC
try: `#!/usr/bin/perl -l # http://perlmonks.org/?node_id=1181779 use strict; use warnings; sub convert { unpack('H*', shift() =~ tr/cd/qr/r) =~ tr/1267/0101/r; } for ( qw( abcd dcba abab cdcd abba caab ) ) { print "$_ -> ", convert($_); }` [download] prints: `abcd -> 00011011 dcba -> 11100100 abab -> 00010001 cdcd -> 10111011 abba -> 00010100 caab -> 10000001` [download]	[reply] [d/l] [select]
Re^2: convert each character of a string to number by haukex (Archbishop) on Feb 12, 2017 at 09:45 UTC
Hi tybalt89, Very clever :-) Building on your idea, this appears to be a bit faster: `$string=~tr/abcd/\x00\x01\x10\x11/; unpack('H*', $string);` Regards, -- Hauke D	[reply] [d/l]
Re: convert each character of a string to number by kcott (Archbishop) on Feb 12, 2017 at 06:00 UTC
G'day Lowry76, Is this the type of thing you're looking for? `$ perl -e 'printf "%02b", ord($_) - ord("a") for split //, "abcd"' 00011011` [download] — Ken	[reply] [d/l]
Re: convert each character of a string to number by poj (Abbot) on Feb 12, 2017 at 16:00 UTC
Consider building a hash of all 256 possible strings. `#!/usr/bin/perl use strict; my %convert=(); my %char = ( '00'=>'a', '01'=>'b', '10'=>'c', '11'=>'d', ); for my $n (0..255){ my $bin = sprintf "%08b",$n; (my $str = $bin) =~ s/(..)/$char{$1}/eg; $convert{$str} = int $bin; } for ( qw( aaaa abcd dcba abab cdcd abba caab dddd) ){ print $_.' '.$convert{$_}."\n"; }` [download] poj	[reply] [d/l]