[SOLVED] gsub for dealing with dates in r in data

gsub for dealing with dates in r in data

I am dealing with very large data set of university students where dates are in the form

%d/%m/%y

I need to work out ages.

My data looks something like this as it was pulled from a database:

data <- data.table(DOB=c("12/12/01", "8/05/80", "2/11/99"), 
                  started =c("5/10/10", "4/01/12", "27/08/11"))

The problem is that for calculating ages the whole year is not specified.

I have tried changing the years to numeric:

data$DOB<-as.Date(data$DOB, "%d/%m/%y")
data$start<-as.Date(data$start, "%d/%m/%y")
data$DOB<-as.numeric(format(data$DOB,"%Y"))
data$start<-as.numeric(format(data$start,"%Y"))
data$age<-data$start-data$dob

Obviously this does not work as I need to add in the 20 and 19.

Is there a way I can use gsub to put a '20' in front of all the where the dob is less than or equal to 15 and a '19' in front of all the dob is more than 15.

I don't think there are any 85 year olds in my dataset.

Solution

And a similar approach using the substr and nchar functions of base R.

library(data.table)

dt <-data.table(DOB=c("12/12/01", "8/05/80", "2/11/99"), 
                started =c("5/10/10", "4/01/12", "27/08/11"))

dt

#         DOB  started
# 1: 12/12/01  5/10/10
# 2:  8/05/80  4/01/12
# 3:  2/11/99 27/08/11


WholeYear = function(x){

            v1 = substr(x, 1, nchar(x)-2)
            v2 = substr(x, nchar(x)-1, nchar(x))

            ifelse(as.numeric(v2) <= 15, paste0(v1,"20",v2), paste0(v1,"19",v2)) 

                        }


dt$DOB = sapply(dt$DOB, WholeYear)
dt$started = sapply(dt$started, WholeYear)

dt


#           DOB    started
# 1: 12/12/2001  5/10/2010
# 2:  8/05/1980  4/01/2012
# 3:  2/11/1999 27/08/2011