convert string date to R Date FAST for all dates

Question

This has been asked several times with no clear answer: I would like to convert an R character string of the form "YYYY-mm-dd" into a Date. The as.Date function is exceedingly slow. convert character to date *quickly* in R provides a solution using fasttime that works for dates from 1970 onward. My issue is I have dates starting from 1900 that I need to convert and there are about 100 million of them. I have to do this frequently so the speed is important. Are there any other solutions?

Answer 1

I can get a little speedup by using the date package:

library(date)
set.seed(21)
x <- as.character(Sys.Date()-sample(40000, 1e6, TRUE))
system.time(dDate <- as.Date(x))
#    user  system elapsed 
#    6.54    0.01    6.56 
system.time(ddate <- as.Date(as.date(x,"ymd")))
#    user  system elapsed 
#    3.42    0.22    3.64 

You might want to look at the C code it uses and see if you can modify it to be faster for your specific situation.