Can't remove the the duplicate element when it's the last one in the array

littlehorse has asked for the wisdom of the Perl Monks concerning the following question:

Replies are listed 'Best First'.
Re: Can't remove the the duplicate element when it's the last one in the array by Ratazong (Monsignor) on Dec 18, 2009 at 09:03 UTC
Your code seems to be too "tricky" (read: complicated) Especially, you should avoid changing variables more than once in a statement. E.g. using `--$i` and `$i++` in `splice @$arr, --$i, 1 if $seen{$arr->[ $i++]}++;` [download] As already recommended by WizardOfUz, you should use `uniq()`. If you want to do it all by yourself, the following code seems to work; `sub remove_dup { my @arr = (1,1); #,2, 1, 3, 1, 4, 3, 1); my %seen; for ( my $i = 0; $i < scalar @arr; $i++){ splice @arr, $i--, 1 if $seen{$arr[ $i]}++; } print @arr, " "; }` [download]	[reply] [d/l] [select]
Re^2: Can't remove the the duplicate element when it's the last one in the array by ikegami (Patriarch) on Dec 18, 2009 at 16:05 UTC
`my %seen; for ( my $i = 0; $i < scalar @arr; $i++){ splice @arr, $i--, 1 if $seen{$arr[ $i]}++; }` [download] can be simplified to `my %seen; for ( my $i = @arr; $i--; ){ splice @arr, $i, 1 if $seen{$arr[$i]}++; }` [download] But the following will be much faster: `my %seen; @arr = grep !$seen{$_}++, @arr;` [download]	[reply] [d/l] [select]
Re^2: Can't remove the the duplicate element when it's the last one in the array by littlehorse (Sexton) on Dec 18, 2009 at 09:15 UTC
Ratazong, I have figured out it's my mistake. Yes, It's more readable to write it in your style, many thanks to you.	[reply]
Re: Can't remove the the duplicate element when it's the last one in the array by WizardOfUz (Friar) on Dec 18, 2009 at 08:51 UTC
Take a look at the `uniq()` function in List::MoreUtils for an elegant (perlish) solution.	[reply] [d/l]
Re: Can't remove the the duplicate element when it's the last one in the array by AnomalousMonk (Archbishop) on Dec 18, 2009 at 11:06 UTC
Take a look at the `uniq()` function ... I second that. Your code seems to be too "tricky" ... Too tricky by half. But if you are going to recommend 'simple' code, at least recommend the idiomatic version: `>perl -wMstrict -le "my @ra = (1, 3, 2, 3, 2, 3, qw{X b X c X}); my %seen; @ra = grep !$seen{$_}++, @ra; print qq{@ra}; " 1 3 2 X b c` [download]	[reply] [d/l] [select]
Re^2: Can't remove the the duplicate element when it's the last one in the array by johngg (Canon) on Dec 18, 2009 at 19:32 UTC
If order need not be preserved I think a hash slice is quicker. `$ perl -MBenchmark=cmpthese -Mstrict -wE ' > my @arr; > push @arr, int rand 20 for 1 .. 1000; > cmpthese( > -5, > { > grep => sub > { > my %seen; > my @uniq = grep ! $seen{ $_ } ++, @arr; > }, > slice => sub > { > my %seen; > @seen{ @arr } = ( 1 ) x @arr; > my @uniq = keys %seen; > }, > } > );' Rate grep slice grep 3041/s -- -29% slice 4260/s 40% -- $` [download] However, take my benchmarks with a pinch of salt, I often make a complete dog's breakfast of them :-( I hope this is of interest. Cheers, JohnGG	[reply] [d/l]
Re^3: Can't remove the the duplicate element when it's the last one in the array by littlehorse (Sexton) on Dec 20, 2009 at 07:46 UTC
johngg, it looks interesting and helpful, I will have a try:)	[reply]
Re^2: Can't remove the the duplicate element when it's the last one in the array by littlehorse (Sexton) on Dec 20, 2009 at 07:43 UTC
AnomalousMonk, your example are very helpful to me, thanks a lot!	[reply]
Re: Can't remove the the duplicate element when it's the last one in the array by JavaFan (Canon) on Dec 18, 2009 at 10:52 UTC
I was using qw{1, 1} to construct the array, You do know that using `qw{1, 1}` triggers a warning, don't you?	[reply] [d/l]
Re^2: Can't remove the the duplicate element when it's the last one in the array by graff (Chancellor) on Dec 18, 2009 at 21:12 UTC
If littlehorse didn't know about the warning, it's most likely because he also doesn't know that this line should have been included somewhere near the top of script file: `use warnings;` [download]	[reply] [d/l]
Re^2: Can't remove the the duplicate element when it's the last one in the array by littlehorse (Sexton) on Dec 20, 2009 at 07:36 UTC
I don't know that will trigger a warning, I'm new to Perl. I forget to use the -w switch when I use the Perl interpreter to execute the script. I will let that switch on next time, thanks.	[reply]