From: Robert Klemme <bob.news@...>
Date: 2006-02-03T19:23:18+09:00
Subject: Re: Seeking the Ruby way

Todd Breiholz wrote:
> I'm just getting my feet wet with Ruby and would like some advice on
> how you "old-timers" would write the following script using Ruby
> idioms.
>
> The intent of the script is to parse a CSV file that contains 2
> fields per row, sorted on the second field. There may be multiple
> rows for field 2. I want to get a list of all of the unique values of
> field2 that has more than 1 value for the 1st 6 characters of field 1.

There are two possible interpretations of what you state here:

1. You want all values for row2 that occur more than once.

2. You want all values for row2 that have more than one distinct row1
value.

Implementations:

ad 1.

require 'csv'

h = Hash.new(0)
CSV::Reader.parse(ARGF) {|row| h[row[1]] += 1}
h.each {|k,v| puts k if v > 1}


ad 2.

require 'csv'
require 'set'

h = Hash.new {|h,k| h[k] = Set.new}
CSV::Reader.parse(ARGF) {|row| h[row[1]] << row[0]}
h.each {|k,v| puts k if v.size > 1}

Note: CSV::Reader can use ARGF which makes it easy to read from stdin as
well as multiple files.

Kind regards

    robert