# Populate (an array or a matrix) from a vector

Discussion in 'Ruby' started by Paul A., Apr 25, 2010.

1. ### Paul A.Guest

Hello,

I have a simple, but very tricky, problem. I would like to fix it using
an array. But matix are possibly more appropriate (even if matrix can
not have 3 dimensional values, I think).

I would like to populate a table (of 2 or 3 dimensions), from a vector.

I think the best way to explain myself is to put some examples, with an
array such as:

And now, if the seeder vector is: [1, 0], the result should be:

=> [
=> [4, 3, 2, 1, 0],
=> [4, 3, 2, 1, 0],
=> [4, 3, 2, 1, 0]
=> ]

If the vector is: [-1, 0]

=> [
=> [0, 1, 2, 3, 4],
=> [0, 1, 2, 3, 4],
=> [0, 1, 2, 3, 4]
=> ]

If the vector is: [-2, 0]

=> [
=> [0, 0, 1, 1, 2],
=> [0, 0, 1, 1, 2],
=> [0, 0, 1, 1, 2]
=> ]

If the vector is: [1, 1]

=> [
=> [2, 2, 2, 1, 0],
=> [1, 1, 1, 1, 0],
=> [0, 0, 0, 0, 0]
=> ]

If the vector is: [0, 1]

=> [
=> [2, 2, 2, 2, 2],
=> [1, 1, 1, 1, 1],
=> [0, 0, 0, 0, 0]
=> ]

Have you got a idea, or a plan? :s
Any comments are welcome. Thank you.

Best regards.

Paul A., Apr 25, 2010

2. ### Rolf PedersenGuest

[Note: parts of this message were removed to make it a legal post.]

Tip: Did you check out the Matrix and Vector classes in the Ruby Standard
Library?
http://ruby-doc.org/core/classes/Matrix.html
http://ruby-doc.org/core/classes/Vector.html

Best regards,
-Rolf

Rolf Pedersen, Apr 25, 2010

3. ### Paul A.Guest

Paul A., Apr 25, 2010
4. ### Colin BartlettGuest

I must confess that from your examples, I'm not at all sure how you
want to populate the "array" given the vector, so the following may
not be any help at all. But: if you want multidimensional numerical
arrays, then NArray might be useful.

http://narray.rubyforge.org
NArray is an Numerical N-dimensional Array class. Supported element
types are 1/2/4-byte Integer, single/double-precision Real/Complex,
and Ruby Object. This extension library incorporates fast calculation
and easy manipulation of large numerical arrays into the Ruby
language. NArray has features similar to NumPy, but NArray has vector
and matrix subclasses. ...

I haven't used it much myself, and I haven't used it recently. But I
did manage to install and use it without using gems, so if I can do it
that way it can't be all that difficult to install !

Colin Bartlett, Apr 26, 2010
5. ### Masahiro TANAKAGuest

Hi,
I guessed your intention and wrote it using NArray:

require 'narray'

def populate( shape, v )
ndim = shape.size
max = shape.max
a = NArray.int(ndim,*shape)
shape.each_with_index do |sz,i|
if v == 0
a[i,false] = max
else
r = [1]*ndim
r = sz
x = NArray.int(sz).indgen!
x = sz-1-x if v > 0
x /= v.abs
a[i,false] = x.reshape!(*r)
end
end
a.min(0)
end

populate( [5,3], [1,0] )
=> NArray.int(5,3):
[ [ 4, 3, 2, 1, 0 ],
[ 4, 3, 2, 1, 0 ],
[ 4, 3, 2, 1, 0 ] ]

populate( [5,3], [-1,0] )
=> NArray.int(5,3):
[ [ 0, 1, 2, 3, 4 ],
[ 0, 1, 2, 3, 4 ],
[ 0, 1, 2, 3, 4 ] ]

populate( [5,3], [-2,0] )
=> NArray.int(5,3):
[ [ 0, 0, 1, 1, 2 ],
[ 0, 0, 1, 1, 2 ],
[ 0, 0, 1, 1, 2 ] ]

populate( [5,3], [1,1] )
=> NArray.int(5,3):
[ [ 2, 2, 2, 1, 0 ],
[ 1, 1, 1, 1, 0 ],
[ 0, 0, 0, 0, 0 ] ]

populate( [5,3], [0,1] )
=> NArray.int(5,3):
[ [ 2, 2, 2, 2, 2 ],
[ 1, 1, 1, 1, 1 ],
[ 0, 0, 0, 0, 0 ] ]

populate( [5,3,3], [2,1,1] )
=> NArray.int(5,3,3):
[ [ [ 2, 1, 1, 0, 0 ],
[ 1, 1, 1, 0, 0 ],
[ 0, 0, 0, 0, 0 ] ],
[ [ 1, 1, 1, 0, 0 ],
[ 1, 1, 1, 0, 0 ],
[ 0, 0, 0, 0, 0 ] ],
[ [ 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0 ],
[ 0, 0, 0, 0, 0 ] ] ]

Masahiro Tanaka

Masahiro TANAKA, Apr 27, 2010
6. ### Paul A.Guest

Thank you very much, Masahiro Tanaka! Your response is exactly what I
dreamed of doing. And your numerical n-dimensional array class is
absolutly awesome! I'm glad to continue coding with!

Thanks again.
Best regards.

Paul A., Apr 27, 2010