Hi Martin,
It kind of does make sense to issue the warning when **recycling** (and
this is consistent with what happens with recycling in general):
> matrix(1:4, 6, 6)
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] 1 3 1 3 1 3
[2,] 2 4 2 4 2 4
[3,] 3 1 3 1 3 1
[4,] 4 2 4 2 4 2
[5,] 1 3 1 3 1 3
[6,] 2 4 2 4 2 4
> matrix(1:4, 5, 6)
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] 1 2 3 4 1 2
[2,] 2 3 4 1 2 3
[3,] 3 4 1 2 3 4
[4,] 4 1 2 3 4 1
[5,] 1 2 3 4 1 2
Warning message:
In matrix(1:4, 5, 6) :
data length [4] is not a sub-multiple or multiple of the number of
rows [5]
(Note that the warning is misleading. matrix() is happy to take data
with a length that is not a sub-multiple of the number of rows or cols
as long as it's a sub-multiple of the length of the matrix.)
However I'm not sure that **truncating** the data is desirable behavior:
> matrix(1:6, 1, 3)
[,1] [,2] [,3]
[1,] 1 2 3
> matrix(1:6, 1, 5)
[,1] [,2] [,3] [,4] [,5]
[1,] 1 2 3 4 5
Warning message:
In matrix(1:6, 1, 5) :
data length [6] is not a sub-multiple or multiple of the number of
columns [5]
Maybe you get a warning sometimes, if you are lucky, but still.
Finally note that you never get any warning with array():
> array(1:4, c(5, 6))
[,1] [,2] [,3] [,4] [,5] [,6]
[1,] 1 2 3 4 1 2
[2,] 2 3 4 1 2 3
[3,] 3 4 1 2 3 4
[4,] 4 1 2 3 4 1
[5,] 1 2 3 4 1 2
> array(1:6, c(1, 5))
[,1] [,2] [,3] [,4] [,5]
[1,] 1 2 3 4 5
Cheers,
H.
On 2/1/21 1:08 AM, Martin Maechler wrote:
Abby Spurdle (/əˈbi/)
on Mon, 1 Feb 2021 19:50:32 +1300 writes:
> I'm a little surprised that the following doesn't trigger an error or a
warning.
> matrix (1:256, 8, 8)
> The help file says that the main argument is recycled, if it's too short.
> But doesn't say what happens if it's too long.
It's somewhat subtler than one may assume :
matrix(1:9, 2,3)
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
Warning message:
In matrix(1:9, 2, 3) :
data length [9] is not a sub-multiple or multiple of the number of rows [2]
matrix(1:8, 2,3)
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
Warning message:
In matrix(1:8, 2, 3) :
data length [8] is not a sub-multiple or multiple of the number of columns
[3]
matrix(1:12, 2,3)
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
So it looks to me the current behavior is quite on purpose.
Are you sure it's not documented at all when reading the docs
carefully? (I did *not*, just now).
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Hervé Pagès
Bioconductor Core Team
hpages.on.git...@gmail.com
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