CODEWITHSUNDEEP
rmatrix
user1320502
user1320502

Reputation: 2570

dyadic maximum in matrices

Imagine you have the matrix mat:

mat <- matrix(c(0,2,3,3,0,1,1,1,0), nrow = 3,byrow=TRUE)
rownames(mat) <- list("a","b","c")
colnames(mat) <- list("a","b","c")
mat
#  a b c
#a 0 2 3
#b 3 0 1
#c 1 1 0

I want to find the which of the upper and lower triangle pairs are the biggest. e.g. b:a is >than a:b and a:c is >than c:a.

I then want to return a mtrix where the cell with the biggest value in the pair gets a 1 and evrything else, smaller values and ties get a zero. The result for mat would be:

result <- matrix(c(0,0,1,1,0,0,0,0,0), nrow = 3,byrow=TRUE)
rownames(result ) <- list("a","b","c")
colnames(result ) <- list("a","b","c")
result
# a b c
#a 0 0 1
#b 1 0 0
#c 0 0 0

Upvotes: 0

Views: 27

Answers (1)

G. Grothendieck
G. Grothendieck

Reputation: 269852

Try this:

> (mat > t(mat)) + 0
  a b c
a 0 0 1
b 1 0 0
c 0 0 0

To return 0.5 for ties:

> (mat > t(mat)) + .5 * (mat == t(mat))
    a   b   c
a 0.5 0.0 1.0
b 1.0 0.5 0.5
c 0.0 0.5 0.5

Upvotes: 1

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