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Re: Divide a list of string into substrings (updated)

by AnomalousMonk (Bishop)
on Jun 20, 2020 at 20:15 UTC ( #11118284=note: print w/replies, xml ) Need Help??


in reply to Divide a list of string into substrings

I don't understand all the business about scoring, but at least this gets the expected fields for the given input strings. Perhaps you can use it as a point of departure to achieve your true goals.

c:\@Work\Perl\monks>perl -wMstrict -le "use Test::More 'no_plan'; use Test::NoWarnings; ;; use Data::Dump qw(dd); ;; use List::MoreUtils qw(uniq); ;; my @list = ( 'set abcde-efghi 12345', 'set abcde-ijkl 12345', 'clr abcde-efghi+123', 'clr abcde-ijkl 12345', ); ;; my @expected_substrings = ( 'set', 'clr', ' abcde-', 'efghi', 'ijkl', ' 12345', '+123', ); ;; my $rx_fld1 = qr{ [[:alpha:]]{2,} }xms; my $rx_fld2 = qr{ \s [[:alpha:]]{2,} - }xms; my $rx_fld3 = qr{ [[:alpha:]]{3,} }xms; my $rx_fld4 = qr{ [\s+] [[:digit:]]{2,} }xms; ;; my (@flds1, @flds2, @flds3, @flds4); for my $str (@list) { my $parsed = my ($fld1, $fld2, $fld3, $fld4) = $str =~ m{ \A ($rx_fld1) ($rx_fld2) ($rx_fld3) ($rx_fld4) \z }xms; die qq{'$str' parse failed} unless $parsed; ;; push @flds1, $fld1; push @flds2, $fld2; push @flds3, $fld3; push @flds4, $fld4; } ;; my @got_substrings = uniq @flds1, @flds2, @flds3, @flds4; dd \@got_substrings; ;; is_deeply \@got_substrings, \@expected_substrings, 'extracted list ok'; " ["set", "clr", " abcde-", "efghi", "ijkl", " 12345", "+123"] ok 1 - extracted list ok ok 2 - no warnings 1..2
Note: uniq is also in List::Util in up-to-date versions of Perl; I'm testing under version 5.8.9.

Update: It occurs to me that the uniq-ifying step should be done on each sub-set individually before the sub-sets are combined together. This could be done with a
    my @got_substrings = map { uniq @$_ } \(@flds1, @flds2, @flds3, @flds4);
statement. The output list produced is the same.


Give a man a fish:  <%-{-{-{-<

Replies are listed 'Best First'.
Re^2: Divide a list of string into substrings (updated)
by Anonymous Monk on Jun 21, 2020 at 09:18 UTC

    Thanks for the nice script !

    The example should just illustrate the problem. The strings in the list can be completely different and your solution will only work with this specific example.

    There even might exists a better solution (with a lower score ($len)) for this example as the given one. I am looking for an idea how to come to a good and fast solution, accepting that this solution is not the best one, which can be found. (See also the answer of Bill)

      I suspect there is no "good and fast" solution. This problem, to me, has the flavor of a permutation or "traveling salesman" problem, and is probably NP-hard (or one of the other NP classes).

      So here's an attempt (with a cheat) that at least gets a solution in a sort of reasonable time for this problem.

      #!/usr/bin/perl use strict; # https://perlmonks.org/?node_id=11118281 use warnings; my @list=("set abcde-efghi 12345", "set abcde-ijkl 12345", "clr abcde-efghi+123", "clr abcde-ijkl 12345"); #my @expected_substrings=("set","clr"," abcde-","efghi", # "ijkl"," 12345","+123"); #my $len=@expected_substrings*2; #$len+=length($_) foreach @expected_substrings; $_ = join "\n", @list; my $max = 3; ########################################### BIG CHEAT FOR + RUNTIME sub score { 2 * @_ + length join '', @_; } my $best = score( @list ); try( $_ ); print "\n"; sub try { (local $_, my @sofar) = @_; if( !/[ -~]/ ) { my $score = score @sofar; if( $score < $best ) { print "\n"; use Data::Dump 'dd'; dd $score, @sofar; $best = $score; } return; } score(@sofar) >= $best and return; for my $n ( reverse 0 .. $#list ) { my %d; /([ -~]{3,})(?:.*?\1){$n}(?{ $d{$1}++ })(*FAIL)/s; my @d = sort { length $b <=> length $a } sort keys %d; @d > $max and $#d = $max - 1; for my $string ( @d ) { try( s/\Q$string\E/\t/gr, @sofar, $string ); } } }

      Outputs:

      (46, " abcde-", " 12345", "efghi", "ijkl", "clr", "set", "+123")

      where the "46" is the score and the rest are the substrings. As it finds better scores, it will print them, but so far always seems to find a best solution first.

        Many thanks for this nice solution.

        Especially I like the way you search for equal substrings: /([ -~]{3,})(?:.*?\1){$n}(?{ $d{$1}++})(*FAIL)/s;

        I will use a lot of your ideas in my solution ...

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