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Re^3: incrementing already existing file

by roboticus (Chancellor)
on Feb 28, 2011 at 02:57 UTC ( #890498=note: print w/replies, xml ) Need Help??


in reply to Re^2: incrementing already existing file
in thread incrementing already existing file

wanttoprogram:

OK, are both files sorted with respect to the key fields? If so, then you don't really want nested loops. You want a single loop and you can decide which file to read depending on what the current condition is. Something like:

# "Prime the pump" my $rec1 = <FILE1>; my $rec2 = <FILE2>; # Keep looping as long as either file has records while (!eof(FILE1) or !eof(FILE2)) { # Figure out what keys you have my $key1 = get_key_1($rec1); my $key2 = get_key_2($rec2); if ($key1 eq $key2) { # They're the same, so create an output record, and read # next record from file2 print build_record($rec1, $rec2); $rec2 = <FILE2>; } elsif ($key1 lt $key2) { # First file has a key we don't need, just ignore # it and read the next record $rec1 = <FILE1>; } else { # Hmmm ... first file seemed to skip the key we need. # print a partial record and advance to next file2 record print partial_record($rec2); $rec2 = <FILE2>; } }

Of course, if either of the files aren't sorted on the keys, then that won't work. You'll either have to sort them, or try something like a hash table. For the hash table, you simply read the first file into a hash based on the key field(s). Then you scan through the second file, looking up values from the hash as you need them. Something like:

# Read dictionary my %abbreviations; while (my $line = <DATA>) { my ($abbrev,$longname) = split/:/, $line; $abbreviations{$abbrev}=$longname; } # Process file open my $FH, '<', 'the_file' or die; while (my $line = <$FH>) { my ($field1, $field2, $key, $field3) = split /\t/, $line; if (exists $abbreviations{$key}) { # key was abbreviated, replace with full value $key = $abbreviations{$key}; } print "$key: ($field1, $field2, $field3)\n"; } close $FH; __DATA__ perl:pathologically eclectic rubbish lister lisp:lots of irritating silly parenthesis python:all your space are belong to us ruby:a quack language

...roboticus

When your only tool is a hammer, all problems look like your thumb.

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