Re: what is Vector#map2 ?

On 2013-07-05, at 2:49 PM, [e-mail] wrote:

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

--=20

Mike Stok <[e-mail]>
http://www.stok.ca/~mike/

The "`Stok' disclaimers" apply.