From: "David A. Black" <dblack@...>
Date: 2009-01-04T22:37:06+09:00
Subject: Re: Default values of hashes

Hi --

On Sun, 4 Jan 2009, Glenn wrote:

> I actually have a followup question to this one.

It turns out that sometimes I will need to go more than two levels deep with the hashes.  I inferred that to go three levels deep, the code would be:

h = Hash.new{|h,k| h[k]= Hash.new{|h2,k2| h2[k2]= Hash.new{|h3,k3| h3[k3]=0}}}

This works fine.  It seems, though, that I might have to go more
levels deep than this.  I am trying to look for a way to do this
dynamically within a method.  In other words, if I need 3 levels, it
creates a hash within hash object 3 levels deep (like in the line of
code above) and if I need 5, it creates one 5 levels deep.  I do not
know how to do this (or even if it is possible).  Any suggestions on
this one?

It's come up before; here's the solution I seem to recall:

hproc = lambda {|h,k| h[k] = Hash.new(&hproc) }
hash = Hash.new(&hproc)

hash[1][2][3] = 4
p hash             # {1=>{2=>{3=>4}}}


David

-- 
David A. Black / Ruby Power and Light, LLC
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