Cannot assign names when converting matrix using as.data.frame - r

Question

I want to generate a two-column data frame that has a given correlation. Two columns named "x" and "y". There are tons of ways to do this, sampling from a multivariate normal distribution being one. So, for 50 rows of correlation r = 0.95, this works:
myFrame <- as.data.frame(mvrnorm(10, mu = c(0,0), Sigma = matrix(c(1,0.56,0.56,1),, ncol = 2), empirical = TRUE))
myFrame
...but you'll notice that the column names are V1 and V2. I've read what I think is relevant in the docs, but I can't get the names to change.
I've tried using col.names = c("x", "y") in various places. It seems it would go between the final two closed parentheses, but I've tried other places. Even though I didn't think it correct, I tried names = c("x, y") as well, to no avail.
I understand I could use a second step to change the names, but since as.data.frame() accepts a vector to name the columns, I shouldn't have to resort to that.

Answer 1

As pointed out in comments, neither data.frame() nor the matrix method for as.data.frame have an argument to let you set column names.
The standard way, as you say, would be to set the names of the object in a second line of code. If that is abhorrent to you, you can still get it done in a single line. Here are two options:
myFrame1 = as.data.frame("colnames<-"(mvrnorm(10, mu = c(0,0), Sigma = matrix(c(1, 0.56, 0.56, 1), ncol = 2), empirical = TRUE), c("x", "y")))
myFrame2 = setNames(as.data.frame(mvrnorm(10, mu = c(0,0), Sigma = matrix(c(1, 0.56, 0.56, 1), ncol = 2), empirical = TRUE)), c("x", "y"))
# I would prefer using two lines, much clearer:
myFrame3 = as.data.frame(mvrnorm(10, mu = c(0,0), Sigma = matrix(c(1, 0.56, 0.56, 1), ncol = 2), empirical = TRUE))
names(myFrame3) = c("x", "y")
# Or, if you're a fine of pipes:
library(magrittr)
myFrame4 = mvrnorm(
10,
mu = c(0,0),
Sigma = matrix(c(1, 0.56, 0.56, 1), ncol = 2),
empirical = TRUE
) %>%
as.data.frame %>%
setNames(c("x", "y"))
When looking at ?as.data.frame, these are the methods described:
## S3 method for class 'character'
as.data.frame(x, ...,
stringsAsFactors = default.stringsAsFactors())
## S3 method for class 'list'
as.data.frame(x, row.names = NULL, optional = FALSE, ...,
cut.names = FALSE, col.names = names(x), fix.empty.names = TRUE,
stringsAsFactors = default.stringsAsFactors())
## S3 method for class 'matrix'
as.data.frame(x, row.names = NULL, optional = FALSE,
make.names = TRUE, ...,
stringsAsFactors = default.stringsAsFactors())
Notice that the matrix method does not have a col.names argument. Only the list method does. So in converting a list to a data.frame, you can use col.names, but not converting a matrix.