From: "marcandre (Marc-Andre Lafortune)" <ruby-core@...>
Date: 2012-08-11T02:29:16+09:00
Subject: [ruby-core:47119] [ruby-trunk - Feature #6852] [].transpose should behave specially


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


Hi,

> boris_stitnicky (Boris Stitnicky) wrote:
> > In other words, when [] is the receiver, ... it should raise,
> > or warn, or complain
> 
> Strictly speaking you are right.

Oups, I was not thinking straight. [] corresponds to a 0x0 matrix (i.e. Matrix[] or Matrix.empty(0,0)). It is its own transpose.

So the current behavior is correct.

What could be said is that `[[], [], []].transpose` is not completely accurate in returning [], but no other result is possible. For more accurate handling... use the matrix library.

I'll close this if there are no other objections.
----------------------------------------
Feature #6852: [].transpose should behave specially
https://bugs.ruby-lang.org/issues/6852#change-28769

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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