3

I have two matrices in R, a square matrix, and a non-square matrix:

dataMatrix1, a 5x5 matrix:

1 2 3 4 3
2 1 3 5 7
3 3 1 1 8
4 5 1 1 5
1 7 8 5 1

dataMatrix2, a 5x8 matrix:

1 0.2 0.3 0.4 0.3 0.9 0.6 0.5
0.2 1 0.3 0.5 0.7 0.8 0.6 0.1
0.3 0.3 1 0.1 0.8 0.3 0.1 0.6
0.4 0.5 0.1 1 0.5 0.3 0.1 0.7
0.1 0.7 0.8 0.5 1 0.5 0.9 0.9

I want to replace the lower triangular part of the first 5x5 elements of dataMatrix2 with the lower triangular of dataMatrix1, so I would get the following matrix:

1 0.2 0.3 0.4 0.3 0.9 0.6 0.5
2   1 0.3 0.5 0.7 0.8 0.6 0.1
3   3   1 0.1 0.8 0.3 0.1 0.6
4   5   1   1 0.5 0.3 0.1 0.7
1   7   8   5   1 0.5 0.9 0.9

I just made up the values of these matrices to use as an example, I have to do this for a couple of matrices. Is there a systematic way to achieve this?

data

m1 <-"
1 2 3 4 3
2 1 3 5 7
3 3 1 1 8
4 5 1 1 5
1 7 8 5 1"
m1 <- as.matrix(read.table(text=m1,h=F))

m2 <-"
1 0.2 0.3 0.4 0.3 0.9 0.6 0.5
0.2 1 0.3 0.5 0.7 0.8 0.6 0.1
0.3 0.3 1 0.1 0.8 0.3 0.1 0.6
0.4 0.5 0.1 1 0.5 0.3 0.1 0.7
0.1 0.7 0.8 0.5 1 0.5 0.9 0.9"
m2 <- as.matrix(read.table(text=m2,h=F))
moodymudskipper
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Abdel
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1 Answers1

4

You can use lower.tri() function - it works correctly on both matrices:

mat1 <- matrix(1:25, nrow=5)
mat2 <- matrix(rnorm(50), nrow=5)

Here is the result of lower.tri:

> lower.tri(mat1)
      [,1]  [,2]  [,3]  [,4]  [,5]
[1,] FALSE FALSE FALSE FALSE FALSE
[2,]  TRUE FALSE FALSE FALSE FALSE
[3,]  TRUE  TRUE FALSE FALSE FALSE
[4,]  TRUE  TRUE  TRUE FALSE FALSE
[5,]  TRUE  TRUE  TRUE  TRUE FALSE

> lower.tri(mat2)
      [,1]  [,2]  [,3]  [,4]  [,5]  [,6]  [,7]  [,8]  [,9] [,10]
[1,] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[2,]  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[3,]  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[4,]  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
[5,]  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE FALSE

And you can use it for replacement:

mat2[lower.tri(mat2)] <- mat1[lower.tri(mat1)]
mat2
> mat2
         [,1]       [,2]       [,3]       [,4]        [,5]       [,6]        [,7]       [,8]        [,9]       [,10]
[1,] 1.217691  0.3217439  1.2819224 -0.8618631  0.42995995  1.6090869 -0.01434864  1.4435626 -0.49071287  0.24014275
[2,] 2.000000  0.9499850 -0.8694622 -0.4298002 -0.18049240 -0.4742643  0.66824074  0.5185916  0.08725232 -0.38885167
[3,] 3.000000  8.0000000 -0.4522152 -1.1518328 -0.97425214 -0.1934794 -1.21050069 -0.3670091 -1.08416208  0.65378101
[4,] 4.000000  9.0000000 14.0000000 -0.7285091 -0.75610467  2.7866430 -0.63774276 -1.3474289 -0.25998202  1.57901406
[5,] 5.000000 10.0000000 15.0000000 20.0000000 -0.07180773 -0.5519527  0.29733510  0.7673501 -1.78309776  0.04265967
Karolis Koncevičius
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