From: Mike Stok <mike@...>
Date: 2013-07-06T03:59:42+09:00
Subject: Re: what is Vector#map2 ?


On 2013-07-05, at 2:49 PM, sto.mar@web.de wrote:

> Am 05.07.2013 20:25, schrieb Love U Ruby:
>> Hi,
>> 
>> Can anyone give me one example to understand the functionality of
>> Vector#map2(http://yard.ruby-doc.org/stdlib-2.0/Vector.html#collect2-instance_method).
>> I understand the Vector#map.
>> 
>> require 'matrix'
>> 
>> a = [1, 2, 3, 4]
>> m = Vector[*a] # => Vector[1, 2, 3, 4]
>> m.map{|i| i * i } # => Vector[1, 4, 9, 16]
> 
> Shouldn't be too difficult to find out by looking at the source,
> but anyway:
> 
> 2.0.0p247 :007 > u = Vector[1, 2, 3]
> => Vector[1, 2, 3]
> 2.0.0p247 :008 > v = Vector[7, 8, 9]
> => Vector[7, 8, 9]
> 2.0.0p247 :009 >  u.collect2(v) {|e1, e2| e1*e2 }
> => [7, 16, 27]

With pry (and pry-plus) it is easy to get to the source and docs for a method:

[1] pry(main)> require 'matrix'
=> true
[2] pry(main)> $ Vector#collect2

From: /Users/mike/.rbenv/versions/2.0.0-p247/lib/ruby/2.0.0/matrix.rb @ line 1630:
Owner: Vector
Visibility: public
Number of lines: 8

def collect2(v) # :yield: e1, e2
  raise TypeError, "Integer is not like Vector" if v.kind_of?(Integer)
  Vector.Raise ErrDimensionMismatch if size != v.size
  return to_enum(:collect2, v) unless block_given?
  Array.new(size) do |i|
    yield @elements[i], v[i]
  end
end
[3] pry(main)> ri Vector#collect2
Vector#collect2

(from ruby core)
------------------------------------------------------------------------------
  collect2(v) { |e1, e2| ... }

------------------------------------------------------------------------------

Collects (as in Enumerable#collect) over the elements of this vector and
v in conjunction.


[4] pry(main)>

Hope this helps,

Mike

-- 

Mike Stok <mike@stok.ca>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.