Re: Is it possible to make reference to substrings and sort them?

Using chop could be another way to go.

$ perl -Mstrict -Mwarnings -E '
say join q{},
   map { substr $_, -1 }
   sort
   sub {
       my $s = shift;
       my @r;
       push @r, do {
          $s = chop( $s ) . $s;
          $s;
          } for 1 .. length $s;
       return @r;
       }->( q{BANA$} );'
ANB$A
$
[download]

I think I read somewhere that chop is fast so it might be worth benchmarking.

Cheers,

JohnGG

Comment on Re: Is it possible to make reference to substrings and sort them? Download Code

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Re^2: Is it possible to make reference to substrings and sort them? by AnomalousMonk (Archbishop) on Mar 22, 2015 at 19:19 UTC
I thought of a similar approach, but as BrowserUk pointed out above, if a list of all rotations of a 5,000,000 character string must be generated and stored somewhere, it's going to crash and burn. Anyway, FWIW: `c:\@Work\Perl\monks>perl -wMstrict -le "use Test::More 'no_plan'; ;; my $t = 'BANA$'; ;; my @rots = do { my $u = $t; map $u = chop($u) . $u, 1 .. length $u } ; ;; my $ar_expected = [ reverse qw(BANA$ ANA$B NA$BA A$BAN $BANA) ]; is_deeply \@rots, $ar_expected, 'cyclic rotations'; ;; my $bwt = join '', map chop, sort @rots ; ;; is $bwt, 'ANB$A', qq{'$t' -> '$bwt' transform}; " ok 1 - cyclic rotations ok 2 - 'BANA$' -> 'ANB$A' transform 1..2` [download] The generation of the `@rots` array is broken out into a separate step just so it can be tested against the OPed data; normally, it would be part of the sort operation chain. Give a man a fish: `<%-(-(-(-<`	[reply] [d/l] [select]

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Re^2: Is it possible to make reference to substrings and sort them?
by AnomalousMonk (Archbishop) on Mar 22, 2015 at 19:19 UTC

I thought of a similar approach, but as BrowserUk pointed out above, if a list of all rotations of a 5,000,000 character string must be generated and stored somewhere, it's going to crash and burn. Anyway, FWIW:

c:\@Work\Perl\monks>perl -wMstrict -le
"use Test::More 'no_plan';
 ;;
 my $t = 'BANA$';
 ;;
 my @rots =
   do { my $u = $t;  map $u = chop($u) . $u, 1 .. length $u }
   ;
 ;;
 my $ar_expected = [ reverse qw(BANA$ ANA$B NA$BA A$BAN $BANA) ];
 is_deeply \@rots, $ar_expected, 'cyclic rotations';
 ;;
 my $bwt =
   join '',
   map chop,
   sort
   @rots
   ;
 ;;
 is $bwt, 'ANB$A', qq{'$t' -> '$bwt' transform};
"
ok 1 - cyclic rotations
ok 2 - 'BANA$' -> 'ANB$A' transform
1..2
[download]

@rots

sort

Give a man a fish: <%-(-(-(-<

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