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Re^2: How to save first two columns of an array into another array

by zing (Beadle)
on Oct 02, 2012 at 14:05 UTC ( #996863=note: print w/replies, xml ) Need Help??

in reply to Re: How to save first two columns of an array into another array
in thread How to save first two columns of an array into another array

Ok and how do I read the same (i.e. those first two columns into a hash). this is what I tried.
my %h; my @a = map { [@{ $_ }[0]] } @S; my @b = map { [@{ $_ }[1]] } @S; @h{@a} = @b; print Dumper(@a); print Dumper(@b); print Dumper(%h); print "or\n"; print Dumper(\%h);
But the output is wrong
$VAR1 = { 'ARRAY(0x8411210)' => [ 'e' ], 'ARRAY(0x840d768)' => [ 'c' ], 'ARRAY(0x83f3308)' => [ 'c' ] };

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Re^3: How to save first two columns of an array into another array
by Athanasius (Chancellor) on Oct 02, 2012 at 14:25 UTC

    Is this what you wanted?

    my %h = map { $_->[0] => $_->[1] } @S; print Dumper(\%h);


    $VAR1 = { 'a' => 'c', 'b' => 'c', 'd' => 'e' };

    Note: Once you put the data into a hash, the original order of the keys is lost. This is the way hashes work.

    Hope that helps,

    Athanasius <°(((><contra mundum

      Thanks all. So after introducing corrections suggested by you,I achieved at this code below. It operates on the same data file and outputs the connected components.But the problem is that the last part of the code i.e. the connected components part isnt working well.

      If I enable "use strict" i get this error :- "Can't use string ("c") as an ARRAY ref while "strict refs" in use at line 44, <> line 3." Line 44 being this "for my $tgt ( \@{ $h{$src} } ) {"

      Whereas if I disable "use strict" i get incomplete output for the connected components as :

      ----connected components--------------- - d: [] - a: [] b: []
      The correct output should be this
      ----connected components--------------- - d: [e] - a: [c] b: [c]
      My second question is that how can I access each of these connected components separately as per my need(i.e. either of them).
      #This program read the triplets from file named "data" into #an array of array. #use strict; use warnings; use Data::Dumper; use Graph; use Graph::Subgraph; # use PDL; my @S; while (<>) { push @S, [ split ]; } print "#########TRIPLETS#####\n"; print Dumper \@S; print "\n$S[0][1]\n"; # Find the number of vertices my @L; for my $i ( 0 .. $#S ) { for my $j ( 0 .. $#{ $S[$i] } ) { #print "elt $i $j is $S[$i][$j]\n"; push (@L,$S[$i][$j]); } } my %seen; @L = grep { ! $seen{ $_ }++ } @L; print "########VERTICES##########\n"; print Dumper \@L; # Now lets generate the G(L) # In order to generate the G(L) we'll extract first two columns of S i +nto another matrix my @GL=@S; splice(@$_, 2, 1) foreach @GL; print Dumper \@GL; my %h = map { $_->[0] => $_->[1] } @S; print Dumper(\%h); ##### CONNECTED COMPONENTS ########## my $g = Graph->new( undirected => 1 ); for my $src ( keys %h ) { for my $tgt ( \@{ $h{$src} } ) { $g->add_edge($src, $tgt); } } my @subgraphs = $g->connected_components; my @allgraphs; my $V = $g->vertices; print "\n$V\n"; for my $subgraph ( @subgraphs ) { push @allgraphs, {}; for my $node ( @$subgraph ) { if ( exists $h{ $node } ) { $allgraphs[-1]{$node} = [ @{ $h{$node} } ]; } } } print "----connected components------------"; use YAML; print Dump \@allgraphs;

        I can’t find any module named Graph::Subgraph on CPAN or meta::cpan. When I comment out the line use Graph::Subgraph; and run the code, I get the error you describe. The strict pragma is telling you that the syntax is wrong, so removing strict here would merely make the problem harder to identify!

        I’m not sure what the code in this for loop is meant to achieve, but perhaps something as simple as

        for my $src (keys %h) { $g->add_edge($src, $h{$src}); }

        will do what you want? If so, that leads to another, similar, "strict refs" error in the line $allgraphs[-1]{$node} = [ @{ $h{$node} } ];. But since I don’t understand what this final for loop is doing, I’m afraid I can’t offer any help here.  :-(

        Tip: In future, please show the minimum code that demonstrates the problem, and explain exactly what the code is intended to do. Comment the code liberally. See How do I post a question effectively?.

        Update: Just discovered, this issue has been re-addressed in Finding connected components in a graph..

        Athanasius <°(((><contra mundum

Re^3: How to save first two columns of an array into another array
by Anonymous Monk on Oct 02, 2012 at 14:27 UTC
    In your code above, you are creating @a & @b as arrays of references to (one element) arrays. Perhaps what you intend is something like:
    my @a = map { ${ $_ }[0] ] @S;

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