From: Robert Klemme <shortcutter@...>
Date: 2010-01-07T00:20:13+09:00
Subject: Re: group in the array

On 01/06/2010 03:56 PM, Ralf Mueller wrote:
> Robert Klemme wrote:
>> 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
>>
> Looks good, but I could not find it in the online documentation on 
> ruby-doc.org? (Array,Enumerable)

That's weird.  I found it immediately:

group_by
http://ruby-doc.org/core-1.8.7/classes/Enumerable.html#M001150

inject
http://ruby-doc.org/core-1.8.7/classes/Enumerable.html#M001147

Cheers

	robert


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