From: dblack@...
Date: 2007-07-10T21:12:09+09:00
Subject: Re: Beautiful Code : Pity he didn't ask here...

Hi --

On Tue, 10 Jul 2007, John Carter wrote:

> In Example 4.3 he has...
> 1 counts = {}
> 2 counts.default = 0
>
> Personally I prefer...
> counts = Hash.new(0)
>  or
> counts = Hash.new{|hash,key| hash[key]=0}
> buts that's personal preference I guess.

Yes, but be careful: your two lines don't do the same thing as each
other:

irb(main):007:0> counts = Hash.new(0)
=> {}
irb(main):008:0> counts["hi"]
=> 0
irb(main):009:0> counts
=> {}
irb(main):010:0>  counts = Hash.new{|hash,key| hash[key]=0}
=> {}
irb(main):011:0> counts["hi"]
=> 0
irb(main):012:0> counts
=> {"hi"=>0}

> In example 4.4 he rightly identifies line 10 as a little ugly and bemoans the 
> lack of sort_by_value in hash.
>  10 keys_by_count = counts.keys.sort { |a, b| counts[b] <=> counts[a] }
> it seems he doesn't know about..
>
> count.keys.sort_by{|key| count[key]}
>
> Of course he could have done...
>
> class Hash
>  def sort_keys_by_value
>    keys.sort_by{|key| fetch(key)}
>  end
> end

It's best not to get into changing the core language, though, if the
book isn't going to discuss the benefits and pitfalls of doing so in
depth.


David

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