How to get a result of the correct class when concatenating data in R? -

i have found c , rbind class of result based on class of first argument. has caused problem me because presence of na first argument coerces date vectors numeric vectors. compare result of these 2 class calls:

x <- sys.date() y <- na class(c(x, y)) # "date" class(c(y, x)) # "numeric" 

and likewise rbind:

x <- data.frame(column=sys.date()) y <- data.frame(column=na) class(rbind(x, y)$column) # "date" class(rbind(y, x)$column) # "numeric" 

how can ensure result of these concatenations date vector, regardless of order of arguments?

coerce first argument desired class:

c(as.date(y), x) c(as.date(x), y)