Re: Sorting a "tuple" by the second value

[Anonymous Monk]

Use sort, example at sorting CSV files

[thmsdrew]

Thanks for that link, it was helpful for sure. Here's how I did it. The first subroutine gets the tuples from the file, splits them into an array, and writes them all into one array.

sub get_links {
    my @links;
    open(my $fh, "<", "links.alpha.sorted.25sample")
        or die "cannot open < links.alpha.sorted.25sample: $!";
    while(<$fh>) {
        chomp;
        my $tuple;
        @$tuple = split(/\s+/, $_);
        push(@links, $tuple);
    }
    return @links;
}

Then I sort by the second value and write it to another file:

sub sort_and_store {
    my @links = get_links();
    my @sorted_links = sort { $a->[1] cmp $b->[1] } @links;
    open(my $fh, ">", "sorted.by.destination")
        or die "cannot open > sorted.by.destination: $!";
    foreach my $tuple (@sorted_links) {
        print $fh "@$tuple\n";
    }
}

I've never used the @$blah variable type before, and I couldn't find any information about it. I'm guessing that's how you refer to the arrays in an array of arrays?

[johngg]

You could combine the steps in your get_links() and sort_and_store() subroutines into one process.

knoppix@Microknoppix:~$ cat spw964070.in
abc peter
def jack
ghi zak
jkl ben
mno mick
pqr alan
knoppix@Microknoppix:~$ perl -Mstrict -wE '
> open my $inFH, q{<}, q{spw964070.in}
>    or die qq{open: < spw964070.in: $!\n};
> open my $outFH, q{>}, q{spw964070.out}
>    or die qq{open: > spw964070.out: $!\n};
> 
> print $outFH
>    map  { $_->[ 0 ] }
>    sort { $a->[ 2 ] cmp $b->[ 2 ] }
>    map  { [ $_, split ] }
>    <$inFH>;
> 
> close $inFH 
>    or die qq{close: < spw964070.in: $!\n};
> close $outFH
>    or die qq{close: > spw964070.out: $!\n};'
knoppix@Microknoppix:~$ cat spw964070.out 
pqr alan
jkl ben
def jack
mno mick
abc peter
ghi zak
knoppix@Microknoppix:~$

Sticking to your subroutines, it would be more efficient for get_links() to return a reference to @info than the huge array itself, like so:-

    ...
    return \ @links;
}

sub sort_and_store {
    my $refToLinks = get_links();
    my @sorted_links = sort { $a->[1] cmp $b->[1] } @$refToLinks;
    ...

I hope these points are helpful.

[thmsdrew]

Definitely helpful. I need to learn more about referencing and when it's best to use. Thanks!

[Anonymous Monk]

I've never used the @$blah variable type before, and I couldn't find any information about it. I'm guessing that's how you refer to the arrays in an array of arrays?

Yes, that is one way to do it, known as dereferenceing because $blah is a reference, see references quick reference

Its nice you picked up a new trick, but I would still use sort :)

$ cat fafafile
3       6       1
1       2       0
9       1       9
4       4       5
7       3       2
0       5       4
6       7       6
2       9       8

$ sort --dictionary-order  fafafile
0       5       4
1       2       0
2       9       8
3       6       1
4       4       5
6       7       6
7       3       2
9       1       9

$ sort --dictionary-order --key=2,2 fafafile
9       1       9
1       2       0
7       3       2
4       4       5
0       5       4
3       6       1
6       7       6
2       9       8

[thmsdrew]

Wow, that is a lot easier than my way. It takes longer but I also had to take the time to write the program in the first place! Thank you kind sir!