That is a fine section of 'The R Inferno'
but I don't think it applies to your problem.
The answer to your question in the subject line
is obviously "yes". It happens when the matrix
(or more generally any array) is of mode "list".
A useful example of this is in Circle 8.1.8.
http://www.burns-stat.com/pages/Tutor/R_inferno.pdf
In your case you can do things like:
> M[[1,1]]
[1] "aaa"
> M[[1,2]]
[1] "bbb"
> M[[2,2]]
[1] 0.274498
But not:
> M[[,2]]
Error in M[[, 2]] : invalid subscript type 'symbol'
Pat
On 17/04/2012 05:13, Worik R wrote:
After a lot of processing I get a matrix into M. I expected each row and
column to be a vector. But it is a list.
R-Inferno says...
"Arrays (including matrices) can be subscripted with a matrix of positive
numbers. The subscripting matrix has as many columns as there are dimensions
in the array—so two columns for a matrix. The result is a vector (not an
array)
containing the selected items."
My version of R:
version.string R version 2.12.1 (2010-12-16)
Here is an example...
Qm<- c("aaa", "bbb", "ccc")
DF<- data.frame(Name=sample(Qm, replace=TRUE, size=22), Value=runif(22),
stringsAsFactors=FALSE)
M<- sapply(Qm, function(nm, DF){last(DF[DF[, "Name"]==nm,])}, DF)
class(M)
[1] "matrix"
class(M[,1])
[1] "list"
class(M[1,])
[1] "list"
M
aaa bbb ccc
Name "aaa" "bbb" "ccc"
Value 0.4702648 0.274498 0.5529691
DF
Name Value
1 ccc 0.99948920
2 aaa 0.51921281
3 aaa 0.10803943
4 aaa 0.82265847
5 ccc 0.83237260
6 bbb 0.88250933
7 aaa 0.41836131
8 aaa 0.66197290
9 ccc 0.01911771
10 ccc 0.99994699
11 bbb 0.35719884
12 ccc 0.86274858
13 bbb 0.57528579
14 aaa 0.12452158
15 aaa 0.44167731
16 aaa 0.11660019
17 ccc 0.55296911
18 aaa 0.12796890
19 bbb 0.44595741
20 bbb 0.93024768
21 aaa 0.47026475
22 bbb 0.27449801
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--
Patrick Burns
pbu...@pburns.seanet.com
twitter: @portfolioprobe
http://www.portfolioprobe.com/blog
http://www.burns-stat.com
(home of 'Some hints for the R beginner'
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