How do I convert date to number of days in R

Question

How do I convert date to number of days, starting from the first day of the year.

How do I convert the following to the expected result below?

   Dat         


        

Answer 1

Load your dataset

df <- structure(list(Date = structure(c(1L, 4L, 2L, 3L), .Label = c("02/01/2000", 
"12/12/2000", "13/01/2001", "20/02/2000"), class = "factor"), 
    Date2 = structure(c(10958, 11007, 11303, 11335), class = "Date"), 
    NumDays = structure(c(1, 50, 346, 378), units = "days", class = "difftime")), .Names = c("Date", 
"Date2", "NumDays"), row.names = c(NA, -4L), class = "data.frame")

Format dates:

startdate <- as.Date("01/01/2000","%d/%m/%Y")
df$Date2 <-  as.Date(df$Date,"%d/%m/%Y")

Use difftime to calculate the difference in days

df$NumDays  <- difftime(df$Date2,startdate ,units="days")

df

         Date      Date2  NumDays
# 1 02/01/2000 2000-01-02   1 days
# 2 20/02/2000 2000-02-20  50 days
# 3 12/12/2000 2000-12-12 346 days
# 4 13/01/2001 2001-01-13 378 days