Re: Re: Slowness when inserting into pre-extended array

[liz]

Some remarks on the code in the while loop:

   $line=~/^(\S*) [0-9.]* (.*)$/o;

The /o modifier is not necessary, as the string to match is already a constant and is therefor already compiled at compile time. From perldoc perlop:

PATTERN may contain variables, which will be interpolated (and the pattern recompiled) every time the pattern search is evaluated, except for when the delimiter is a single quote. (Note that $(, $), and $| are not interpolated because they look like end-of-string tests.) If you want such a pattern to be compiled only once, add a "/o" after the trailing delimiter. This avoids expensive run-time recompilations, and is useful when the value you are interpolating won't change over the life of the script. However, mentioning "/o" constitutes a promise that you won't change the variables in the pattern. If you change them, Perl won't even notice.

   my ($class, $feature_vector) = ($1, $2);

Are you sure that the regex will always match? If not, you may introduce duplicates for each time there's no match. From perldoc perlre:

NOTE: failed matches in Perl do not reset the match variables, which makes easier to write code that tests for a series of more specific cases and remembers the best match.

Liz

[ryangabbard]

re: /o
Thanks!
re: will regexp always match?
Yes - it's taken directly from some other code that reads the same file format with no problem.

[tilly]

How do you know that the other code didn't have silent errors on 5 lines out of 300,000? It is free to put a check that will blow up if you fail to match, and being in the habit of testing implicit assumptions is never a bad thing.