Unique list of hashes

mrguy123 has asked for the wisdom of the Perl Monks concerning the following question:

Hi monks
Haven't asked a question in a while but this is an interesting case (also I really need to solve it).
Say I have a list of hashes, for example:

@students = (
{
   name  => "Guy",
   college => "Yale",
},
{
   name  => "Gil",
   college => "Harvard",
},
{
   name  => "Gil",
   college => "Harvard",
},
);
[download]

I want to make this list unique, meaning it needs to look like this:

@uniq_students = (
{
   name  => "Guy",
   college => "Yale",
},
{
   name  => "Gil",
   college => "Harvard",
},
);
[download]

List::MoreUtils::uniq doesn't work on lists of hashes so that's a no go. I can do it for one hash key (below) but for 2 or more keys it's tricky

##Solution for one hash key
my @unique = do { my %seen; grep { !$seen{$_->{name}}++ } @students};
[download]

Of course I can find a workaround (e.g. make each hash into a string and then sort ...) but I would like to try and find something better (and shorter) if possible
Any ideas?

Everybody seems to think I'm lazy
I don't mind, I think they're crazy
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Re: Unique list of hashes by hdb (Monsignor) on Mar 02, 2015 at 11:29 UTC
Like this? `use strict; use warnings; use Data::Dumper; my @students = ( { name => "Gil", college => "Yale", }, { name => "Gil", college => "Harvard", }, { name => "Gil", college => "Harvard", }, ); my @unique = do { my( %seenName, %seenCollege ); grep { !$seenName{$_->{name}}++ or !$seenCollege{$_->{college}}++ +} @students}; print Dumper \@unique;` [download] UPDATE: Sorry, got that wrong. It should be: `my @unique = do { my %seen; grep { !$seen{$_->{name}}{$_->{college}}++ } @students};` [download]	[reply] [d/l] [select]
Re^2: Unique list of hashes by mrguy123 (Hermit) on Mar 02, 2015 at 11:36 UTC
Nice!! I was actually thinking along the line of your first solution, but couldn't get figure out how to take care of the "or". I think this is just what I need. Thanks!	[reply]
Re: Unique list of hashes by LanX (Saint) on Mar 02, 2015 at 11:37 UTC
As a side note: I suggest you better try to find a unique identifier for each student and restructure your data: `%students = ( 1111 => { name => "Guy", college => "Yale", }, 2222 => { name => "Gil", college => "Harvard", }, );` [download] Keep in mind that equally named persons are not that rare, even in the same university. Cheers Rolf _{(addicted to the Perl Programming Language and ☆☆☆☆ :)} PS: Je suis Charlie!	[reply] [d/l]
Re: Unique list of hashes by parv (Parson) on Mar 02, 2015 at 11:41 UTC
Make a key out of combined values to search for uniqueness ... `@uniq = grep !$seen{ join '' , sort values %{ $_ } }++ , @list ;` [download]	[reply] [d/l]
Re^2: Unique list of hashes by Anonymous Monk on Mar 02, 2015 at 11:57 UTC
Make a key out of combined values to search for uniqueness ... `@uniq = grep !$seen{ join '' , sort values %{ $_ } }++, @list;` So these are all the same? `my @list = ( { foo=>'bar', quz=>'baz' }, { abc=>'bar', def=>'baz' }, { ijk=>'ba', xyz=>'rbaz' }, { r=>'ba', s=>'rba', t=>'z' }, { x=>'barbaz' }, );` [download]	[reply] [d/l] [select]
Re^3: Unique list of hashes by hdb (Monsignor) on Mar 02, 2015 at 12:05 UTC
Using a delimiter that cannot appear in the values would be useful... like a pipe or such.	[reply]
Re^3: Unique list of hashes by parv (Parson) on Mar 02, 2015 at 12:24 UTC
Nope, not all are same as you already know. hdb has already given slightly complicated method to satisfy your situation.	[reply]


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