R help - Feb 2015 - naming rows/columns in 'array of matrices'

Suppose I have the following situation:

I have an array of 2 matrices, where each matrix is (2x2):

P <- array(0, c(2,2,2))

P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);

I want to label rows and columns of each matrix in the array, such that 
P would look like


         live dead
live      1    2
dead      3    4

, , 2

         live  dead
  live     5    6
  dead     7    8

I've tried 'direct, brute force" approaches like

rownames(P[,,1]) <- c("live","dead")
colnames(P[,,1]) <- c("live","dead")

(repeated for the second matrix), but this doesn't work.

Since all of the matrices are of the same dimension(s), and since I want 
the same rownames and colnames for each matrix, I'm hoping there is some 
simply magical permutation of lapply (I'm guessing) which will do the trick.

  I'd also be interested in why the 'direct, brute force' approach 
(above) doesn't work, and what does, since I might need to manipulate 
row/col names for individual matrices in the array (if, say, dimensions 
of the matrices were not the same over the array).

Thanks in advance!

The (obvious, after the fact) solution at the bottom. D'oh...

On 1/30/2015 2:07 PM, Evan Cooch wrote:
> Suppose I have the following situation:
>
> I have an array of 2 matrices, where each matrix is (2x2):
>
> P <- array(0, c(2,2,2))
>
> P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
> P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);
>
> I want to label rows and columns of each matrix in the array, such 
> that P would look like
>
>
>         live dead
> live      1    2
> dead      3    4
>
> , , 2
>
>         live  dead
>  live     5    6
>  dead     7    8
>
> I've tried 'direct, brute force" approaches like
>
> rownames(P[,,1]) <- c("live","dead")
> colnames(P[,,1]) <- c("live","dead")
>
> (repeated for the second matrix), but this doesn't work.
>
> Since all of the matrices are of the same dimension(s), and since I 
> want the same rownames and colnames for each matrix, I'm hoping there 
> is some simply magical permutation of lapply (I'm guessing) which will 
> do the trick.
Forgot I was dealing with a multi-dimensional array, not a list. So, 
following works fine. I'm sure there are better approaches (where 
'better' is either 'cooler', or 'more flexible'), but
for the moment...)

P <- array(0, 
c(2,2,2),dimnames=list(c("live","dead"),c("old","young"),NULL))

P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);

print(P);

> On 30 Jan 2015, at 20:34 , Evan Cooch <evan.cooch at gmail.com>
wrote:
> 
> The (obvious, after the fact) solution at the bottom. D'oh...
> 
[snip]
> Forgot I was dealing with a multi-dimensional array, not a list. So,
following works fine. I'm sure there are better approaches (where
'better' is either 'cooler', or 'more flexible'), but
for the moment...)
> 
> P <- array(0,
c(2,2,2),dimnames=list(c("live","dead"),c("old","young"),NULL))
> 
> P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
> P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);
> 
> print(P);
> 
Just for completeness, this also works:
> P <- array(0, c(2,2,2)) 
> P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
> P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);
> dimnames(P)[[1]] <- c("live","dead")
> dimnames(P)[[2]] <- c("live","dead")

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
Phone: (+45)38153501
Email: pd.mes at cbs.dk  Priv: PDalgd at gmail.com

In your example, P is a three dimensional array.  You can assign names to
the three dimensions using the dimnames() function.  For example, this
command assigns names to the first two dimensions, but leaves the third
dimension without names.

dimnames(P) <- list(c("live", "dead"),
c("live", "dead"), NULL)

Jean

On Fri, Jan 30, 2015 at 1:07 PM, Evan Cooch <evan.cooch at gmail.com>
wrote:
> Suppose I have the following situation:
>
> I have an array of 2 matrices, where each matrix is (2x2):
>
> P <- array(0, c(2,2,2))
>
> P[,,1] <- matrix(c(1,2,3,4),2,2,byrow=T);
> P[,,2] <- matrix(c(5,6,7,8),2,2,byrow=T);
>
> I want to label rows and columns of each matrix in the array, such that P
> would look like
>
>
>         live dead
> live      1    2
> dead      3    4
>
> , , 2
>
>         live  dead
>  live     5    6
>  dead     7    8
>
> I've tried 'direct, brute force" approaches like
>
> rownames(P[,,1]) <- c("live","dead")
> colnames(P[,,1]) <- c("live","dead")
>
> (repeated for the second matrix), but this doesn't work.
>
> Since all of the matrices are of the same dimension(s), and since I want
> the same rownames and colnames for each matrix, I'm hoping there is
some
> simply magical permutation of lapply (I'm guessing) which will do the
trick.
>
>  I'd also be interested in why the 'direct, brute force'
approach (above)
> doesn't work, and what does, since I might need to manipulate row/col
names
> for individual matrices in the array (if, say, dimensions of the matrices
> were not the same over the array).
>
> Thanks in advance!
>
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> >  I'd also be interested in why the 'direct, brute force'
approach
> > (above) doesn't work,
Your example was a 3-dimensional array, so 
> rownames(P) <- colnames(P) <- c(live', 'dead') 
would have worked; rownames() and colnames() work on dimnames[1] and
dimnames[2].

But 
rownames(P[,,1])
could not have worked, because you were not assigning to the names of P; you
were assigning to something (P[,,1]) extracted from P. In effect, you were doing
the equivalent of
{P1 <- P[,,1]
rownames(P1) <- c('live', 'dead')
rm(P1)}

> > ... since I might need to manipulate
> > row/col names for individual matrices in the array (if, say,
> > dimensions of the matrices were not the same over the array).
If the dimension are different you will not have an array; you'd have to
have a list of matrices.
You could then use lapply for the one constant dimension size; for example, 

lp <- list(P22 = matrix(ncol=2, nrow=2), P32= matrix(ncol=2, nrow=3))

lapply(lp, function(x, cn=c('live', 'dead'))
{colnames(x)<-cn; x})

Other than that, you'd either have to do some careful conditional coding or
apply names manually.

S


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