[r] How to coerce a list object to type 'double'

The code:

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

Then a is like

$`X$Days`
[1] "10"  "38"  "66"  "101" "129" "185" "283" "374"

I would like to coerce a to an array of numeric values, but coercing functions return me

Error: (list) object cannot be coerced to type 'double'

Thanks,

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]])

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

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]}

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)))
}