Re: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1

edit - this is essentially the same as Tybalt's entry in 1229444, which I missed when posting.

Here's one that is adapted from Discipulus and haukex3. Using a binary search will speed up the search for the inflection point, while pushing and splicing in one pass avoids repeated pushes. It should scale better as the data increases in size.

The binary search needs a recent version of List::MoreUtils. I've specified the latest here, but one could go somewhat older I think. One could also use List::BinarySearch::XS

    swl => sub {
        my @list = @input;
        use List::MoreUtils 0.428;
        @list = sort {$a<=>$b} @list;
        my $i = List::MoreUtils::bsearchidx {$_ <=> 0} @list;
        push @list, splice @list, 0, $i-1;
        Compare(\@list,\@output) or die "@list" if DO_CHECK;
    }
[download]

Comment on Re: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 Download Code

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Re^2: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 by tybalt89 (Monsignor) on Feb 06, 2019 at 06:31 UTC
Would this work if 1) There is no 0 in the list ? 2) There are several 0, Would it pick the correct (earliest) one ?	[reply]
Re^3: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 by swl (Prior) on Feb 06, 2019 at 23:58 UTC
Thanks for checking. It fails if there were three or more zeroes (the test case provided has two zeroes), and if there are no zeroes. Adding some extra checks seems to fix the issues, and is still close to try1a for speed given the provided test data (sometimes as fast but usually a few percent slower). `swl2 => sub { my @list = @input; use List::MoreUtils 0.428; @list = sort {$a<=>$b} @list; my $i = List::MoreUtils::bsearchidx {$_ <=> 0} @list; if ($i < 0) { # no zero $i = List::MoreUtils::firstidx {$_ >= 0} @list; } else { $i-- while !$list[$i]; $i++; } push @list, splice @list, 0, $i; Compare(\@list,\@output) or die "@list" if DO_CHECK; },` [download] It will be slower in cases where there are no zeroes, although List::BinarySearch::binsearch_pos could be used to find an insert point for zero in such cases.	[reply] [d/l]
Re^4: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 by swl (Prior) on Feb 07, 2019 at 00:53 UTC
Another update to handle lists where all values are >= 0 (as flagged in 1229492). Also using the while loop instead of List::MoreUtils::firstidx based on the benchmarks in that post. EDIT - added check for upper bound being >=0, borrowing from code in 1229437. `swl3 => sub { my @list = @input; use List::MoreUtils 0.428; @list = sort {$a<=>$b} @list; if ($list[0] < 0 && $list[-1] >= 0) { my $i = List::MoreUtils::bsearchidx {$_ <=> 0} @list; if ($i < 0) { # no zero, find first positive $i = 0; $i++ while ($list[$i]<0); } else { # find start of zeroes $i-- while !$list[$i]; $i++; } push @list, splice @list, 0, $i; } Compare(\@list,\@output) or die "@list" if DO_CHECK; },` [download]	[reply] [d/l]
Re^2: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 by swl (Prior) on Feb 06, 2019 at 02:54 UTC
And if non-core modules aren't permitted, then this adaptation of haukex3 can be used: `swl2 => sub { my @list = @input; @list = sort {$a<=>$b} @list; my $i = 0; $i++ while ($list[$i]<0); push @list, splice @list, 0, $i; Compare(\@list,\@output) or die "@list" if DO_CHECK; },` [download]	[reply] [d/l]
Re^3: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1 by swl (Prior) on Feb 07, 2019 at 01:40 UTC
Updated for lists that are all negative, following Discipulus4 in 1229492. `swl_pp2 => sub { my @list = @input; @list = sort {$a<=>$b} @list; if ($list[0] < 0 && $list[-1] >= 0) { my $i = 0; $i++ while ($list[$i]<0); push @list, splice @list, 0, $i; } Compare(\@list,\@output) or die "@list" if DO_CHECK; },` [download]	[reply] [d/l]