CODEWITHSUNDEEP
rmatlab
George
George

Reputation: 23

Indexing for Multidimensional array in R like as Matlab

I would like ask you something that seems simple but I got stuck... In Matlab page it is explained very well: https://www.mathworks.com/help/matlab/math/multidimensional-arrays.html

However, I didn't find something similar for R. My question is simple: how can I convert this Matlab code to R? Or how can I print the elements of the first row for each dimension of the matrix like as it is done in Matlab?

Matlab:

A=[1:7;8:14;15:21];
A(:,:,2)=[22:28;29:35;36:42];
A(:,:,3)=[43:49;50:56;57:63];
A(:,:,:4)=[64:70;71:77;78:84];

B=A(1,:,:,:)

The code of first rows in R is written:

A<-array(1:84,c(3,7,4))

The last: B<-??

The desired result is:

, , 1
    [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,]  1   2    3    4    5    6    7
, , 2
    [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 22   23   24   25   26   27   28
, , 3
    [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 43   44   45   46   47   48   49
, , 4
    [,1] [,2] [,3] [,4] [,5] [,6] [,7]
[1,] 64   65   66   67   68   69   70

Thank you in advance!

Upvotes: 0

Views: 77

Answers (1)

jogo
jogo

Reputation: 12559

Matlab uses rowwise definition of the elements in A=[1:7;8:14;15:21]; during R uses columnwise in A<-array(1:84, c(3,7,4)). This gives the desired result:

A <- array(NA, c(3,7,4))
A[,,1] <- matrix(c(1:7, 8:14, 15:21), 3, byrow=TRUE)
A[,,2] <- matrix(c(22:28, 29:35, 36:42), 3, byrow=TRUE)
A[,,3] <- matrix(c(43:49, 50:56, 57:63), 3, byrow=TRUE)
A[,,4] <- matrix(c(64:70, 71:77, 78:84), 3, byrow=TRUE)
A[1,, , drop=FALSE]
# > A[1,, , drop=FALSE]
# , , 1
# 
# [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]    1    2    3    4    5    6    7
# 
# , , 2
# 
# [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]   22   23   24   25   26   27   28
# 
# , , 3
# 
# [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]   43   44   45   46   47   48   49
# 
# , , 4
# 
# [,1] [,2] [,3] [,4] [,5] [,6] [,7]
# [1,]   64   65   66   67   68   69   70

or the same: A[drop=FALSE, 1,,]

Upvotes: 1

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