[19076] in s-news-athena
[S] Putting values into matrices: desired behaviour?
daemon@ATHENA.MIT.EDU (Mette Langaas)
Wed Sep 1 02:38:40 1999
Message-Id: <37CCC8DE.A756F3D6@nr.no>
Date: Wed, 01 Sep 1999 08:34:06 +0200
From: Mette Langaas <Mette.Langaas@nr.no>
Reply-To: Mette.Langaas@nr.no
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S-Plus users and experts,
I'm running S-Plus 5.1 on UNIX (but the same behaviour I'm describing is
seen on S-Plus 3.4 R1 for UNIX).
I have first created a matrix with two rows and three columns
> test_matrix(ncol=3,nrow=2)
> test
[,1] [,2] [,3]
[1,] NA NA NA
[2,] NA NA NA
I then want to put values into parts of the matrix, but by mistake I
index outside the matrix (use rows 3-7 when there are only 2 rows).
> ind_matrix(c(1,2,3,4,5,6,7,2,2,2,2,2,2,2),ncol=2)
> ind
[,1] [,2]
[1,] 1 2
[2,] 2 2
[3,] 3 2
[4,] 4 2
[5,] 5 2
[6,] 6 2
[7,] 7 2
> test[ind]_c(3,4,5,6,7,8,9)
> test
[,1] [,2] [,3]
[1,] NA 3 5
[2,] NA 4 6
The first observation is that in addition to correctly putting values 3
ang 4 into position (1,2) and (2,2) the value
5 is put into (1,3) instead of (3,2) as requested and
6 is put into (2,3) instead of (4,3) as requested.
In addition the values 7,8,9 have also been put "somewhere" in the
matrix -- where I can not see them -- unless a convert the matrix into a
vector....
> dim(test)
[1] 2 3
> length(test)
[1] 9
> as.vector(test)
[1] NA NA 3 4 5 6 7 8 9
This new matrix "test" has length=9 which is neq
dim(test)[1]*dim(test)[2].
No error message is produced when I do my test[ind], but when I
try to use test I get into problems, e.g. with t(test):
> t(test)
Problem in t.default(test): length must equal product of dimensions
Use traceback() to see the call stack
Is this the desired behaviour of indexing matrices? What measures can I
take to avoid this behaviour -- e.g. to instead get an error message?
Best regards
Mette Langaas
Norwegian Computing Center
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