How to find 'non-unique' value from array when using 'unique' in perl

Question

my @words = qw(1 2 3 4 4);
my @unique_words = uniq @words;

print @unique_words; # 1 2 3 4

I am interested in finding which value was non-unique, in this case 4. And being able to set it equal to a variable so that I can keep track of which specific value was re-occuring.

I want to do this so I can implement a code that says "if my string contains duplicating value from array completely remove duplicating value from array from string". In this case, if a string contained 1 2 3 4 4. I would like it after the if statement to contain 1 2 3.

@toolic Thanks for the response! How do I print the value that was counted more than once with this implementation of code? — FranceMadrid
– FranceMadrid, Commented Oct 18, 2018 at 18:35

ikegami · Accepted Answer · 2018-10-19 12:26:53Z

2

Counting/finding duplicates is easiest done with a hash:

my %count;
$count{ $_ }++ for @words;
print "$_ occurs more than once\n"
    for grep { $count{ $_ } > 1 } @words;

Finding the values that only occur once is done by looking for the elements in %count that have a count of 1:

my %count;
$count{ $_ }++ for @words;
my @unique_words = grep { $count{ $_ } == 1 } @words;

edited Oct 19, 2018 at 12:26

ikegami

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answered Oct 18, 2018 at 18:34

Corion

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5 Comments

FranceMadrid Over a year ago

Thank you that worked! Is there anyway that I can set $_, equal to a variable that holds the value that occurs more than once? So that I may be able to do comparisons globally in my program? Thank you very much for your guidance in advance.

Corion Over a year ago

What do you mean by "the value that occurs more than once"? There can be more than one value that occurs more than once. The expression grep { $count{ $_ } > 1 } keys %count; returns all the values that occur more than once. You can hold on that list by using my @duplicates = grep { $count{ $_ } > 1 } keys %count; .

ysth Over a year ago

or make the list of only non-duplicated values with my @non_duplicates = grep { $count{$_} == 1 } @words;

FranceMadrid Over a year ago

@ysth Thank you so much. That helped a lot. I think that was what I've been looking for.

FranceMadrid Over a year ago

@Corion Thank you, that helped a lot.

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