identifying duplicate array values. 1

[jez]

hello

I am trying to loop through an array and pick out only individual values.

The following code i wrote works but misses a value in the middle of the array for some reason. I have tried a few things but I can't find why it misses this particular value.

The array values are;-

0801
1001
0301
0801
0601
0701
0701
0701
0701
0701
0701
0701

and the array is called @omonths

here is the code;-

@sortedomonths = sort @omonths;
for($i=0;$i<@sortedomonths;$i++) {
if ($sortedomonths[$i] eq $sortedomonths[$i+1]) {$i+=1;}
else {push @indmonths, $sortedomonths[$i];}
}

the results of a print command produce this;-

0301
0601
0701
1001


as you see 0801 is missing, but I can't figure out why.

Any help would be great.


Cheers

Jez

 

[goBoating]

# I would cheat and use a hash....
# Each time you get a duplicate, it just overwrites any previous instances of that one.

foreach ('0801','1001','0301',
'0801','0601','0701','0701',
'0701','0701','0701','0701','0701')
{ $unique{$_} = 1; }

@sorted_unique_months = sort(keys(%unique));



HTH


keep the rudder amid ship and beware the odd typo

 

[raider2001]

The problem is that you are skipping elements in the array. The problem is the line:

if ($sortedomonths[$i] eq $sortedomonths[$i+1]) {$i+=1;}
If the array is a duplicate, you add 1 to the array index in the &quot;if&quot; line and you also add 1 in the for loop. Thus the two 0801s get skipped. An easy fix is to change the line to:
if ($sortedomonths[$i] eq $sortedomonths[$i+1]) {next;}

 

[Guest_imported]

just put some traces in your code!

@sortedomonths is equal to 1001,301,601,701,701,701,701,701,701,701,801,801
so the last loop will execute the first branch of the test and you will not have 801 in your @indmonths

if you want working code, RTFM, for example:

http://www.antipope.org/charlie/attic/perl/one-liner.html

 

[jez]

Cheers GoBoating and Raider2001,

I have used the 'next' option, mainly because the array is handy because the data is just generated lists of 4 digits like that.

Thanks again

Jez

 

[toolkit]

Two alternative methods, that are quite compact:

1) Using a hash slice:

@unique{@unsorted} = @unsorted;
@sorted = sort keys %unique;

2) Using grep

@sorted = sort grep { ! $seen{$_}++ } @unsorted;

The second method has the advantage of populating the

%seen

hash with the number of occurences of each item in

@unsorted

Happy coding, cheers NEIL

 

[goliath]

Is there a way to find the non-unique (duplicates) instead ?

-Thanks!

 

[justice41]

If you just want to know which values are dupicated, and not how many times they are duplicated you can do either of the following

map { $seen{$_}++ } @array;
my @dupes = grep { $seen{$_} > 1 } keys %seen;

# Or a less standard way

my @dupes = keys %{{ map { $_, $_ } grep { $seen{$_}++ } @array }};

jaa