Condition on multiple lines and big file

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

Ciao guys,

I'm trying to solve the following problem but I'm not sure if perl it's the right tool for it. My data look like this:

Buenos    -    SPN    Buenos    B-GPE
Aires    -    SPN    Aires    I-GPE
Afghanistan    -    SPN    Afghanistan    B-GPE
Europa    -    SPN    Europa    B-GPE
UE    -    I    UE    B-GPE
Italia    -    SPN    Italia    B-GPE
Provincia    -    SS    Provincia    B-GPE
di    -    E    di    I-GPE
Lucca    -    SPN    Lucca    I-GPE
...
[download]

As yoou can see, whene there is an I-GPE it means that the name has to be composed whit the line before (i.e. Buenos Aires); when you have just B-GPE and the following line is also B-GPE, than it means they are different names.

Problem is the file is very big and I can't slurp it all at once.

I would like an output like the following

Buenos Aires
Afghanistan
Italia
...
Provincia di Lucca
[download]

Someone has any idea?

One of Crete's own prophets has said it: 'Cretans are always liars, evil brutes, lazy gluttons'.
He has surely told the truth.

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Re: Condition on multiple lines and big file by kcott (Archbishop) on Dec 06, 2013 at 10:33 UTC
G'day epimenidecretese, "I'm not sure if perl it's the right tool for it." Perl would be an admirable tool for this task. `#!/usr/bin/env perl use strict; use warnings; while (<DATA>) { my ($name, $code) = (split)[0,-1]; print $code eq 'I-GPE' ? " $name" : $. == 1 ? $name : "\n$name"; } print "\n"; __DATA__ Buenos - SPN Buenos B-GPE Aires - SPN Aires I-GPE Afghanistan - SPN Afghanistan B-GPE Europa - SPN Europa B-GPE UE - I UE B-GPE Italia - SPN Italia B-GPE Provincia - SS Provincia B-GPE di - E di I-GPE Lucca - SPN Lucca I-GPE` [download] Output: `Buenos Aires Afghanistan Europa UE Italia Provincia di Lucca` [download] -- Ken	[reply] [d/l] [select]
Re^2: Condition on multiple lines and big file by VincentK (Beadle) on Dec 06, 2013 at 20:09 UTC
Your solution is beautiful. I admire its simplicity.	[reply]
Re: Condition on multiple lines and big file by choroba (Cardinal) on Dec 06, 2013 at 10:28 UTC
No need to slurp the file. Process it line by line, remembering just the name: `my $name = q(); while (<>) { my @cols = split; if ('I-GPE' eq $cols[-1]) { $name .= $cols[0] . ' '; } else { print $name, "\n" if chop $name; $name = $cols[0] . ' '; } } # Do not forget to output the last name. chop $name; print "$name\n";` [download] لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply] [d/l]
Re: Condition on multiple lines and big file by Anonymous Monk on Dec 06, 2013 at 13:33 UTC
And, for simpler situations of the same basic problem, also consider `awk`. This is the original tool from which, in one sense, the earliest Perl interpreters grew. It's still great for text-file munging.	[reply]