I have:
B <- matrix(c(1, 0, 0, 1, 1, 1),
nrow=3,
ncol=2)
and I want:
B
[,1] [,2]
[1,] TRUE TRUE
[2,] FALSE TRUE
[3,] FALSE TRUE
as.logical(B)gives a 1D vector. Is there an idiomatic way to do the matrix type conversion?
I'm currently doing the wordy:
boolVector <- as.logical(B)
m <- nrow(B)
n <- ncol(B)
m <- matrix(boolVector, m , n)
m
mode(B) <- "logical" or "mode<-"(B, "logical"). We can also use storage.mode function.
This workaround is good for two reasons:
I learnt this trick when reading source code of some packages with compiled code. When passing R data structures to C or FORTRAN functions, some type coercion may be required and they often use mode or storage.mode for this purpose. Both functions preserve attributes of R objects, like "dim" and "dimnames" of matrices.
## an integer matrix
A <- matrix(1:4, nrow = 2, dimnames = list(letters[1:2], LETTERS[1:2]))
# A B
#a 1 3
#b 2 4
"mode<-"(A, "numeric")
# A B
#a 1 3
#b 2 4
"mode<-"(A, "logical")
# A B
#a TRUE TRUE
#b TRUE TRUE
"mode<-"(A, "chracter")
# A B
#a "1" "3"
#b "2" "4"
"mode<-"(A, "complex")
# A B
#a 1+0i 3+0i
#b 2+0i 4+0i
str("mode<-"(A, "list")) ## matrix list
#List of 4
# $ : int 1
# $ : int 2
# $ : int 3
# $ : int 4
# - attr(*, "dim")= int [1:2] 2 2
# - attr(*, "dimnames")=List of 2
# ..$ : chr [1:2] "a" "b"
# ..$ : chr [1:2] "A" "B"
Note that mode changing is only possible between legitimate modes of vectors (see ?vector). There are many modes in R, but only some are allowed for a vector. I covered this in my this answer.
In addition, "factor" is not a vector (see ?vector), so you can't do mode change on a factor variable.
f <- factor(c("a", "b"))
## this "surprisingly" doesn't work
mode(f) <- "character"
#Error in `mode<-`(`*tmp*`, value = "character") :
# invalid to change the storage mode of a factor
## this also doesn't work
mode(f) <- "numeric"
#Error in `mode<-`(`*tmp*`, value = "numeric") :
# invalid to change the storage mode of a factor
## this does not give any error but also does not change anything
## because a factor variable is internally coded as integer with "factor" class
mode(f) <- "integer"
f
#[1] a b
#Levels: a b
A matrix is a vector with dim attributes. When we apply as.logical, the dim attributes are lost. It can be assigned with dim<-
`dim<-`(as.logical(B), dim(B))
# [,1] [,2]
#[1,] TRUE TRUE
#[2,] FALSE TRUE
#[3,] FALSE TRUE
Or another option is create a logical condition that preserves the attribute structure
B != 0
Or
!!B