Variable Names based on Number in Character Position in R - r

Question

I'm currently trying to change variable names based on the number in each position of the string.
variables <- c("X0.0.1", "X0.1.0", "X1.0.0", "X0.0.2", "X0.1.1", "X0.2.0", "X1.0.1",
"X1.1.0", "X2.0.0", "X0.0.3", "X0.1.2", "X0.2.1", "X0.3.0", "X1.0.2", "X1.1.1", "X1.2.0",
"X2.0.1","X2.1.0","X3.0.0")
Ideally, I'd have something similar to "X0.0.1" = "x", "X0.1.0" = "y", "X1.0.0" = "z", "X0.0.2" = "xx" is there a way to quickly duplicate the variable if there is a 2 in the position of that number? Or even "X3.0.0" = "zzz"?

Answer 1

I believe the following code does what the question asks for. It uses rep to get the repetitions and then paste them together.
s <- strsplit(substring(variables, 2), "\\.")
sapply(s, function(x){
vec <- c("x", "y", "z")[seq_along(x)]
x <- as.integer(x)
y <- rep(vec, rev(x))
paste(y, collapse = "")
})
# [1] "x" "y" "z" "xx" "xy" "yy" "xz" "yz" "zz" "xxx"
#[11] "xxy" "xyy" "yyy" "xxz" "xyz" "yyz" "xzz" "yzz" "zzz"
Edit.
The following function tries to answer the dialog in the comments. It returns a data.frame with the strings and their degrees. Then it's a matter of sorting by degree/chr.
changeVariable <- function(x, chr = c("x", "y", "z")){
s <- strsplit(substring(x, 2), "\\.")
y <- lapply(s, function(.x){
vec <- chr[seq_along(.x)]
.x <- as.integer(.x)
.y <- rep(vec, rev(.x))
list(chr = paste(.y, collapse = ""),
degree = sum(.x)
)
})
res <- do.call(rbind.data.frame, y)
row.names(res) <- NULL
res
}
res <- changeVariable(variables)
res[order(res$degree, res$chr), ]
Edit 2.
With results pasted with superscripts:
changeVariable2 <- function(x){
s <- strsplit(substring(x, 2), "\\.")
y <- lapply(s, function(.x){
vec <- c("x", "y", "z")[seq_along(.x)]
.x <- rev(as.integer(.x))
.y <- vec[.x != 0]
.x <- .x[.x != 0]
list(chr = paste0(.y, "^", .x, collapse = " "),
degree = sum(.x)
)
})
res <- do.call(rbind.data.frame, y)
row.names(res) <- NULL
res
}