CODEWITHSUNDEEP
r
twhitney
twhitney

Reputation: 25

Fill a matrix in R

I have a matrix with the lower triangle filled and want to fill the upper triangle of the matrix with the lower triangle's matching values.

The code I have been trying is :

    r <-  read.table("rcorrected.csv", header = TRUE, sep = ",", check.names = FALSE)
    m <- as.matrix(r)


m[upper.tri(m, diag = FALSE)] <- m[lower.tri(m, diag= FALSE)]

Output:

Warning message:
In m[upper.tri(m, diag = FALSE)] <- m[lower.tri(m, diag = FALSE)] :
  number of items to replace is not a multiple of replacement length


    structure(m)
            1    2    3    4    5    6    7    8    9   10   11   12
 [1,]  1 1.00   NA   NA   NA   NA   NA   NA   NA   NA   NA   NA   NA
 [2,]  2 0.50 1.00   NA   NA   NA   NA   NA   NA   NA   NA   NA   NA
 [3,]  3 0.57 0.50 1.00   NA   NA   NA   NA   NA   NA   NA   NA   NA
 [4,]  4 0.00 0.04 0.16 1.00   NA   NA   NA   NA   NA   NA   NA   NA

dput(head(m[, c(2,1)]))
    structure(c(1, 0.5, 0.57, 0, 0, 0.23, 1, 2, 3, 4, 5, 6), .Dim = c(6L, 
    2L), .Dimnames = list(NULL, c("1", "")))

Is the matrix m, being read as a list?

Upvotes: 1

Views: 193

Answers (2)

G. Grothendieck
G. Grothendieck

Reputation: 269586

If m is a matrix such as that shown in the Note at the end with the lower triangle filled then this fills the upper triangular part too. 

m2 <- m + t(m)
m2
##      [,1] [,2] [,3] [,4]
## [1,]    0    5    9   13
## [2,]    5    0   10   14
## [3,]    9   10    0   15
## [4,]   13   14   15    0

If the diagonal of m is not 0 then do it this way:

m + t(m) - diag(diag(m))

Note

m <- matrix(c(0, 5, 9, 13, 0, 0, 10, 14, 0, 0, 0, 15, 0, 0, 0, 0), 4)
m
##      [,1] [,2] [,3] [,4]
## [1,]    0    0    0    0
## [2,]    5    0    0    0
## [3,]    9   10    0    0
## [4,]   13   14   15    0

If we are starting with a data frame DF then use as.matrix to convert it first.

DF <- structure(list(V1 = c(0, 5, 9, 13), V2 = c(0, 0, 10, 14), V3 = c(0, 
0, 0, 15), V4 = c(0, 0, 0, 0)), class = "data.frame", row.names = c(NA, 
-4L))
m <- as.matrix(DF)

Upvotes: 1

akrun
akrun

Reputation: 887118

Here, we are assigning with unequal number of observations with diag = TRUE on the rhs of assignment and also the diag = TRUE should be inside the lower.tri and not outside the function

m[upper.tri(m, diag = FALSE)] <- m[lower.tri(m, diag= FALSE)]

Upvotes: 2

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