Error in R apply() function with lubridate - r

Question

I have a simple function like this:
f<-function(x){ ymd_h(x[1]) + (x[2] )}
Here I use ymd_h(), hours() from the lubridate package. But when I try to call this function from apply method like this:
result<-apply(wind.new[,c("date","hors")],1,f)
... where *wind.new is a data frame with date, hors and other columns,
I get the following error:
Error in FUN(newX[, i], ...) : could not find function "ymd_h"
Obviously ymd_h is not visible inside apply(). How would I fix this?
UPDATE:
Actually I have the data frame showed below and want to convert date column to YYYYMMDDHH format and add hors column to it as hours. I thought the best approach will be to use lubridate package and I used above mentioned function for that. But the execution took very long time and the output was not correct. Any hints, please?
date hors u v ws wd
2009070100 1 2.34 -0.79 2.47 108.68
2009070100 2 2.18 -0.99 2.4 114.31
2009070100 3 2.2 -1.21 2.51 118.71
............
2009070100 47 2.3 -2.18 3.17 133.5
2009070100 48 1.93 -1.87 2.69 134.12
2009070112 1 2.77 -0.65 2.85 103.17
.........

Answer 1

I am sure that #DrewSteen's comment regarding loading the lubridate package onto the search path is correct.
I think you will have issues with your function because apply will coerce to matrix and will return the incorrect type (more coercions required)
Changing your function to take the date-time and hours data as separate arguments should help.
library(lubridate)
f <- function(date, hours){ymd_h(date) + hours(hours)}
result <- with(wind.new, f(as.character(date), hors))
ymd_h will be slow as it has to guess the format of the date/time.