From: Robert Klemme <shortcutter@...>
Date: 2010-01-06T23:15:09+09:00
Subject: Re: group in the array

On 01/06/2010 09:45 AM, Kolya17 Kolya17 wrote:
> Hi!
> 
> I have a two-dimensional array Farr.
> 
> Farr.each{ |i| print i}
> 
> output:
> ["200912-829", 9]
> ["200912-893", 3]
> ["200912-893", 5]
> ["200912-829", 1]
> ["200911-818", 6]
> ["200911-893", 1]
> ["200911-827", 2]
> 
> I'm trying to get another two-dimensional array, which would be the
> grouping of the first elements.
> In SQL it would be so:
> 
> select String, sum(Number)
> from Farr
> group by String
> 
> and the resulting array would:
> ["200912-829", 10]
> ["200912-893", 8]
> ["200911-818", 6]
> ["200911-893", 1]
> ["200911-827", 2]
> 
> Help please.
> I apologize for spelling, English is not my native.

There is actually Array#group_by since 1.8.7:

arr.group_by {|date,val| date}.each do |date, items|
   printf "%-20s %6d\n", date, items.inject(0) {|sum,x|sum+x}, "\n"
end

or

arr.inject Hash.new(0) do |gr,(date,val)|
   gr[date] += val
   gr
end.each do |date, sum|
   printf "%-20s %6d\n", date, sum
end

or more down to earth

grouped = Hash.new(0)

arr.each do |date, val|
   grouped[date] += val
end

grouped.each do |date, sum|
   printf "%-20s %6d\n", date, sum
end

Kind regards

	robert

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