How to coerce a list object to type 'double'

Question

The code:

a <- structure(list(`X$Days` = c(\"10\", \"38\", \"66\", \"101\", \"129\", \"185\", \"283\", 
                                 \"374\")), .Names         


        

Answer 1

You can also use list subsetting to select the element you want to convert. It would be useful if your list had more than 1 element.

as.numeric(a[[1]])

Answer 2

In this case a loop will also do the job (and is usually sufficiently fast).

a <- array(0, dim=dim(X))
for (i in 1:ncol(X)) {a[,i] <- X[,i]}

Answer 3

If your list as multiple elements that need to be converted to numeric, you can achieve this with lapply(a, as.numeric).

Answer 4

There are problems with some data. Consider:

as.double(as.character("2.e")) # This results in 2

Another solution:

get_numbers <- function(X) {
    X[toupper(X) != tolower(X)] <- NA
    return(as.double(as.character(X)))
}

Answer 5

If you want to convert all elements of a to a single numeric vector and length(a) is greater than 1 (OK, even if it is of length 1), you could unlist the object first and then convert.

as.numeric(unlist(a))
# [1]  10  38  66 101 129 185 283 374

Bear in mind that there aren't any quality controls here. Also, X$Days a mighty odd name.