From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2012-08-13T21:12:40+09:00
Subject: [ruby-core:47146] [ruby-trunk - Feature #6852] [].transpose should behave specially


Issue #6852 has been updated by marcandre (Marc-Andre Lafortune).


Hi,

alexeymuranov (Alexey Muranov) wrote:
> Then it is not possible to express in the same way a 3 x 0 matrix (or 0 x 3?)  I think this was the reason for the original question.

A 3x0 matrix corresponds to [[], [], []], but there is no correspondence for a 0x3 matrix. So strictly speaking, `[[], [], []].transpose` has no valid answer, but returning `[]` is more useful than raising I believe.

----------------------------------------
Feature #6852: [].transpose should behave specially
https://bugs.ruby-lang.org/issues/6852#change-28827

Author: boris_stitnicky (Boris Stitnicky)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 2.0.0


p = [1, 2, 3]
q = [4, 5, 6]
[p, q].transpose
# => [[1, 4], [2, 5], [3, 6]]
As expected, 2 x 3 vector was converted into 3 x 2.

[p].transpose
# => [[1], [2], [3]]
As expected, 1 x 3 => 3 x 1.

[].transpose
# => []
Unexpected, 0 x 3 did not become 3 x 0: [[], [], []]

In other words, when [] is the receiver, transpose has no way to know
what kind of ** 2 dimensional ** object is it - whether 0 x 3, 0 x 4, 0 x 1
or perhaps 0 x 0. #transpose should not assume it is 0 x 0. It should raise,
or warn, or complain, or require argument for this case, in short, it should
behave differently than today.


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