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perl "vlookup" using a hash?

Posted on 2013-11-11
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Last Modified: 2013-11-11
Hi,

I have a text file with two columns like follows

9781      Person1
978       Person2
9782      Person3

I then have an ID that I want to look up from this file - returning the 2nd column for the first match it finds.

For example, if my ID = “978”, I want it to return “Person2” as I want it to be an exact match against columnA.

ID “9782” would then return “Person3”

Can this be done with a hash and using exist?

(This probably sounds so basic that it reads like a homework question, it’s really not!)
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Question by:yelbow
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4 Comments
 
LVL 26

Expert Comment

by:wilcoxon
ID: 39640133
Yes.  As a one-liner, this would do it.  It can be easily expanded into a script (or portion thereof).
perl -ne '($id,$per) = split; $data{$id} = $per; END { print $data{978}, "\n" if exists($data{978}) }'

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Author Comment

by:yelbow
ID: 39640227
Thanks!  I've realised I need to complicate this further - it seems that ColumnA doesn't always contain a unique value.  For example, the data could be:

9781      Person1
978       Person2
978        Person4
9782      Person3

I think a has requires a unique match on the key (?) and if not returns the last one it finds (?) (at least it seems that way!)

is there a way to return the first match it finds on $id?

(Apologies for extending the question!)
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LVL 26

Accepted Solution

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wilcoxon earned 2000 total points
ID: 39640248
First match
perl -ne '($id,$per) = split; $data{$id} = $per unless exists($data{$id}); END { print $data{978}, "\n" if exists($data{978}) }'

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All matches
perl -ne '($id,$per) = split; $data{$id} = [] unless $data{$id}; push @{$data{$id}}, $per; END { print "@{$data{978}}\n" if exists($data{978}) }'

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Author Closing Comment

by:yelbow
ID: 39640264
Thanks!
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