From: Joel VanderWerf <vjoel@...>
Date: 2007-10-31T07:07:01+09:00
Subject: Re: better way to accumulate totals

ara.t.howard wrote:
> 
> On Oct 30, 2007, at 3:40 PM, Joel VanderWerf wrote:
> 
>> This works...
>>
>> count = Hash.new{|h,k| h[k] = Hash.new{|h1,k1| h1[k1] = 0}}
>> => {}
>> count[:foo][1] += 1
>> => 1
>> count[:foo][1] += 1
>> => 2
>> count[:foo][1] += 1
>> => 3
> 
> oh yeah, of course ;-)  i'm in the habbit of using 'update' from 
> 'inject' where is saves you having to return the hash itself...  shorter 
> is better always.

...but only if returning the hash is the right thing to do. In this 
case, we want the "leaf" value, not the hash:

irb(main):034:0> count = Hash.new{|h,k| h.update k => Hash.new{|hh,kk| 
hh.update kk => 0}}
=> {}
irb(main):035:0> count[:foo][1] += 1
NoMethodError: undefined method `+' for {1=>{}, :foo=>{}}:Hash
         from (irb):35
irb(main):036:0> count
=> {1=>{}, :foo=>{}}

-- 
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407