From: Stefan Rusterholz <apeiros@...>
Date: 2008-01-11T01:54:08+09:00
Subject: Re: About array to hash conversion

Holden Holden wrote:
> yermej wrote:
>> On Jan 9, 3:31�pm, Holden Holden <pyar...@gmail.com> wrote:
>>>
>>> return)?
>> These would only work in one specific case. What would this do?
>> 
>> [1, 2, 3].to_h
> 
> That's why I prefer [key, value] pairs, to avoid any ambiguity.
> 
> However, a theorical [1,2,3].to_h should give the same error than 
> Hash[*array] gives:
> 
> irb(main):002:0> Hash[*[1,2,3]]
> ArgumentError: odd number of arguments for Hash

I disagree. Array#to_hash should work so that hash.to_a.to_hash == hash, 
in other words it should create a hash only if it contains key value 
tuples.

> array.inject({}) {|ha, (k, v)| ha[k] = v; ha}

There's absolutely no advantage using inject like this.
h={}; array.each { |k,v| h[k]=v }
Is less code and faster.

> ar.to_enum(:each_with_index).inject({}) {|h, (v,k)| h[k]=v;h}
Same here
h={}; array.each_with_index { |k,v| h[k]=v }

Personally I use the following code in my lib:
# create a hash from an array with keys and an array with values
# you can set default or provide a block just as with Hash::new
def Hash.zip(keys, values, default=nil, &block)
  hash = block_given? ? Hash.new(&block) : Hash.new(default)
  keys.zip(values) { |k,v| hash[k]=v }
  hash
end

class Array
# create a hash from an array of [key,value] tuples
# you can set default or provide a block just as with Hash::new
# Note: if you use [key, value1, value2, value#], hash[key] will
# be [value1, value2, value#]
  def to_hash(default=nil, &block)
    hash = block_given? ? Hash.new(&block) : Hash.new(default)
    each { |(key, *value)| hash[key]=*value }
    hash
  end
end

Regards
Stefan

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