CODEWITHSUNDEEP
rmatrix
user3067923
user3067923

Reputation: 457

combining three vectors into a 3d matrix object in R

I have data from three axes of a physical object in 3 separate vectors. 

x;y;z 
[1]  4  6  4  6 17 10 13 27 33 19
[1]  3  2  5 13 22 20 23 19 31 14
[1] 21  6 12 35 19 44 34 23 26 33

I want to combine these three vectors into a 3-dimensional matrix (if that exist in R) by simply taking the product of them all. If I had just two axes, say "x" and "y" I could do the following 

outer(x, y, FUN="*")
      [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
 [1,]   12    8   20   52   88   80   92   76  124    56
 [2,]   18   12   30   78  132  120  138  114  186    84
 [3,]   12    8   20   52   88   80   92   76  124    56
 [4,]   18   12   30   78  132  120  138  114  186    84
 [5,]   51   34   85  221  374  340  391  323  527   238
 [6,]   30   20   50  130  220  200  230  190  310   140
 [7,]   39   26   65  169  286  260  299  247  403   182
 [8,]   81   54  135  351  594  540  621  513  837   378
 [9,]   99   66  165  429  726  660  759  627 1023   462
[10,]   57   38   95  247  418  380  437  361  589   266

But, because I have three axes, I am not sure how to do this. Using outer on "x" & "y" and then multiplying that by "z" is not the same as using outer on "x" & "z" and multiplying by "y". The goal after generating the 3D matrix is to then plot the 3D matrix.

I have looked at some other posts like this one, but find it confusing Creating a 3D matrix with R?

Upvotes: 1

Views: 439

Answers (1)

akrun
akrun

Reputation: 887691

We can use outer with Reduce after placing the vectors in a list.

res1 <- Reduce(outer, list(x,y,z))

Or another option is expand.grid with rowProds from library(matrixStats) and then convert the product vector ('v1') into an array.

library(matrixStats)
v1 <- rowProds(as.matrix(expand.grid(x,y,z)))
res2 <- array(v1, dim=c(length(x), length(y), length(z)))
identical(res1, res2)
#[1] TRUE
dim(res2)
#[1] 10 10 10

data

x <- c(4, 6, 4, 6, 17, 10, 13, 27, 33, 19)
y <- c(3, 2, 5, 13, 22, 20, 23, 19, 31, 14)
z <- c(21, 6, 12, 35, 19, 44, 34, 23, 26, 33)

Upvotes: 2

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