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Re: speeding up a hash lookup

by japhy (Canon)
on Mar 28, 2001 at 01:31 UTC ( [id://67646]=note: print w/replies, xml ) Need Help??


in reply to speeding up a hash lookup

I created a caching algorithm for your data set. I'll reproduce it here, with comments.

It works like so. It determines the max value over the +/- 0.3 window for each mass in the range LOW - 0.3 to HIGH + 0.3, and it also remembers WHICH mass it found that intensity at. This way, when it gets to the next number, it knows where to start looking -- there's no need to look BEFORE the highest value for a higher value, since it would've been registered as the highest value.

my $cache = cacheMaxIntensity(\%massint); sub cacheMaxIntensity { my $mi = shift; my ($min, $max); # determine the maximum and minimum masses # in the hash while (my ($m) = each %$mi) { $min = $m if not defined($min) or $min > $m; $max = $m if not defined($max) or $max < $m; } # the "latest mass" is defined as the mass within a # +/- 0.3 range with the highest intensity my $latest = $min - 0.3; my %cache = (); # cycle through all the masses, including # 3 less than the min and 3 greater than the max for (my $m = $min - 0.3; $m <= $max + 0.3; $m += 0.1) { # ensure "ABC.D" format (icky non-integers) $m = sprintf("%.1f", $m); # update the value of $latest if it's too # far away from the current mass $latest = sprintf("%.1f", $m - 0.3) if $m - 0.3 > $latest; # build the range (latest .. current + 0.3) # of other masses to examine for my $d ( map sprintf("%.1f", $_ / 10), (10 * $latest) .. (10 * $m + 3) ) { # set the cached intensity for this mass # to the intensity for $d IF: # there is an intensity for $d # AND # there is no cached intensity yet # OR # the intensity for $d is greater than # the cached value $cache{$m} = [ $mi->{$d}, $latest = $d ] if exists $mi->{$d} and ( not($cache{$m}) or $cache{$m}[0] < $mi->{$d} ); } } # return a reference to the cache return \%cache; }
The corollary function, to get the maximum intensity in a range of +/- 0.3 mass, is rather simple:
my $max_I = maxIntensity($cache, $mass); sub maxIntensity { my ($c, $m) = @_; return $c->{sprintf "%.1f", $m}[0]; }
I hope this helps. It took a bit of time for me to write the caching function, but it appears to hold up to my testing.

japhy -- Perl and Regex Hacker

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