Re^2: Picking up Values By Group

I would use a lookup hash for the indices instead of calling index repeatedly.

holli

When you're up to your ass in alligators, it's difficult to remember that your original purpose was to drain the swamp.

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Re^3: Picking up Values By Group by BrowserUk (Patriarch) on Feb 04, 2009 at 16:47 UTC
instead of calling index repeatedly. The tradeoff is: scanning a 4 character string for a single character. hashing a single character to a 32-bit hash and then performing a modulo 4 operation upon it. Which actually favours the former: `#! perl -slw use strict; use Benchmark qw[ cmpthese ]; our %lookup = ( A=>0, B=>1, C=>2, D=>3 ); our $input = 'ACGT' x 1000; cmpthese -1, { index => q[ our( %lookup, $input ); my $n; $n = index "ACGT", $_ for split '', $input; ], hash => q[ our( %lookup, $input ); my $n; $n = $lookup{ $_ } for split '', $input; ], }; __END__ c:\test>junk5 Rate hash index hash 107/s -- -21% index 135/s 27% --` [download] 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. "Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."	[reply] [d/l]

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Re^3: Picking up Values By Group
by BrowserUk (Patriarch) on Feb 04, 2009 at 16:47 UTC

instead of calling index repeatedly.

The tradeoff is:

scanning a 4 character string for a single character.
hashing a single character to a 32-bit hash and then performing a modulo 4 operation upon it.

Which actually favours the former:

#! perl -slw
use strict;
use Benchmark qw[ cmpthese ];

our %lookup = ( A=>0, B=>1, C=>2, D=>3 );
our $input = 'ACGT' x 1000;

cmpthese -1, {
    index => q[
        our( %lookup, $input );
        my $n;
        $n = index "ACGT", $_ for split '', $input;
    ],
    hash  => q[
        our( %lookup, $input );
        my $n;
        $n = $lookup{ $_ } for split '', $input;
    ],
};

__END__
c:\test>junk5
       Rate  hash index
hash  107/s    --  -21%
index 135/s   27%    --
[download]

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.

"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

[reply]
[d/l]