I have got a question regarding the matlab package for R. Here's what I get
library(matlab)
a = matrix(1:4,2,2)
repmat(a,3,1)
[,1] [,2]
[1,] 1 2
[2,] 3 4
[3,] 1 2
[4,] 3 4
[5,] 1 2
[6,] 3 4
this is what I expect. replicate a three times along the first dimension. but
b = matrix(1:6,2,3)
b
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
repmat(b,3,1)
[,1] [,2]
[1,] 1 2
[2,] 3 4
[3,] 5 6
[4,] 1 2
[5,] 3 4
[6,] 5 6
[7,] 1 2
[8,] 3 4
[9,] 5 6
this is not consistent. I want a 6 by 3 matrix as the one obtained by
rbind(b,rbind(b,b))
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
[3,] 1 3 5
[4,] 2 4 6
[5,] 1 3 5
[6,] 2 4 6
It just appears to be transposing the matrix before doing the stacking. You could just transpose your matrix before sending it into repmat
> repmat(t(b), 3, 1)
[,1] [,2] [,3]
[1,] 1 3 5
[2,] 2 4 6
[3,] 1 3 5
[4,] 2 4 6
[5,] 1 3 5
[6,] 2 4 6
Related
Having a matrix A like:
[,1] [,2] [,3] [,4]
[1,] 1 4 7 6
[2,] 2 5 8 1
[3,] 5 1 7 8
and a matrix B like:
[,1]
[1,] 8
[2,] 6
[3,] 1
[4,] 7
[5,] 5
[6,] 2
[7,] 3
[8,] 4
I want to get create a matrix C similar to A replacing A values with the rank of A values in matrix B. The result should be:
matrix C
[,1] [,2] [,3] [,4]
[1,] 3 8 4 2
[2,] 6 5 1 3
[3,] 5 3 4 1
You can use match and adjust the dimensions:
C <- match(A, B)
dim(C) <- dim(A)
--
Example:
> set.seed(123)
> (A <- matrix(sample(1:8), ncol = 4))
[,1] [,2] [,3] [,4]
[1,] 3 8 4 2
[2,] 6 5 1 7
> (B <- matrix(sample(1:8), ncol= 1))
[,1]
[1,] 5
[2,] 4
[3,] 6
[4,] 3
[5,] 8
[6,] 2
[7,] 1
[8,] 7
> (C <- match(A, B))
[1] 4 3 5 1 2 7 6 8
> (dim(C) <- dim(A))
[1] 2 4
> C
[,1] [,2] [,3] [,4]
[1,] 4 5 2 6
[2,] 3 1 7 8
I have a matrix like this:
mat<-matrix(c(10,45,2,15,3,98,1,7,13),nrow = 3)
mat
[,1] [,2] [,3]
[1,] 10 15 1
[2,] 45 3 7
[3,] 2 98 13
I want to get the indices of ordered values, as what we can get from order(x, arr.idx = T) but applied to a matrix. That is:
[,1] [,2]
1 3
3 1
2 2
2 3
1 1
3 3
1 2
2 1
3 2
Is it there a fast way to do it?
Thank you in advance
You can use
arrayInd(order(mat), dim(mat), dimnames(mat))
# [,1] [,2]
# [1,] 1 3
# [2,] 3 1
# [3,] 2 2
# [4,] 2 3
# [5,] 1 1
# [6,] 3 3
# [7,] 1 2
# [8,] 2 1
# [9,] 3 2
Using the order as index, we rearrange the row and col of 'mat' and cbind it to get the row/column index of the ordered values
i1 <- order(mat)
cbind(row(mat)[i1], col(mat)[i1])
# [,1] [,2]
#[1,] 1 3
#[2,] 3 1
#[3,] 2 2
#[4,] 2 3
#[5,] 1 1
#[6,] 3 3
#[7,] 1 2
#[8,] 2 1
#[9,] 3 2
I want to concatenate each row of a matrix (say m1) with each element of another matrix (m2). Here follows an exmple:
m1 <- t(combn(4,2))
m2 <- matrix(NA,nrow(m1),2)
for(i in 1:nrow(m1)){
m2[i,] <- seq(1,4,1)[-c(m1[i,])]
}
> m1
[,1] [,2]
[1,] 1 2
[2,] 1 3
[3,] 1 4
[4,] 2 3
[5,] 2 4
[6,] 3 4
> m2
[,1] [,2]
[1,] 3 4
[2,] 2 4
[3,] 2 3
[4,] 1 4
[5,] 1 3
[6,] 1 2
The matrix that I want should be like this:
> m3
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 1 2 4
[3,] 1 3 2
[4,] 1 3 4
[5,] 1 4 2
[6,] 1 4 3
[7,] 2 3 1
[8,] 2 3 4
[9,] 2 4 1
[10,] 2 4 3
[11,] 3 4 1
[12,] 3 4 2
What is the best practice in this case?
As per the expected output, the logic seems to be that we are expanding the rows of the first dataset by also includng the second dataset, so the number of rows should be double as of the first. In the current approach, we used rep to expand the rows and then cbind with the vector created from the second matrix
cbind(m1[rep(1:nrow(m1), each = 2),], c(t(m2)))
# [,1] [,2] [,3]
# [1,] 1 2 3
# [2,] 1 2 4
# [3,] 1 3 2
# [4,] 1 3 4
# [5,] 1 4 2
# [6,] 1 4 3
# [7,] 2 3 1
# [8,] 2 3 4
# [9,] 2 4 1
#[10,] 2 4 3
#[11,] 3 4 1
#[12,] 3 4 2
I’m looking for a code to create matrix B from matrix A, this is a very simple example my real matrix A is (500 x500) and B11(50x50)
1 2 = A
3 4
1 1 | 2 2
1 1 | 2 2
.----------= B
3 3 | 4 4
3 3 | 4 4
Thanks in advance.
You want a Kronecker product, which is %x%:
R>A <- matrix(1:4,2,2)
R>A
[,1] [,2]
[1,] 1 3
[2,] 2 4
R>X <- matrix(1,2,2)
R>X
[,1] [,2]
[1,] 1 1
[2,] 1 1
R>A %x% X
[,1] [,2] [,3] [,4]
[1,] 1 1 3 3
[2,] 1 1 3 3
[3,] 2 2 4 4
[4,] 2 2 4 4
R>t(A) %x% X
[,1] [,2] [,3] [,4]
[1,] 1 1 2 2
[2,] 1 1 2 2
[3,] 3 3 4 4
[4,] 3 3 4 4
How can I bind the same vector o = c(1,2,3,4) multiple times to get a matrix like:
o = array(c(1,2,3,4,1,2,3,4,1,2,3,4), dim(c(4,3))
[,1] [,2] [,3]
[1,] 1 1 1
[2,] 2 2 2
[3,] 3 3 3
[4,] 4 4 4
In a nicer way than: o = cbind(o,o,o) and maybe more generalized (duplicate)? I need this to specify colors for elements in textplot.
R recycles. It's very eco-friendly:
o=c(1,2,3,4)
> matrix(o,nrow = 4,ncol = 4)
[,1] [,2] [,3] [,4]
[1,] 1 1 1 1
[2,] 2 2 2 2
[3,] 3 3 3 3
[4,] 4 4 4 4
You can use replicate
> o = c(1,2,3,4)
> replicate(4, o)
[,1] [,2] [,3] [,4]
[1,] 1 1 1 1
[2,] 2 2 2 2
[3,] 3 3 3 3
[4,] 4 4 4 4
You can use outer
outer(1:4,1:4,function(x,y)x)
[,1] [,2] [,3] [,4]
[1,] 1 1 1 1
[2,] 2 2 2 2
[3,] 3 3 3 3
[4,] 4 4 4 4