Convert integer as “20160119” to different columns of “day” “year” “month”

Question

How can I convert a column of integers as dates:

       DATE PRCP
1: 19490101   25
2: 19490102    5
3: 19490118   18
4: 19490119  386
5: 19490202   38
         


        

Answer 1

Here's another way using regular expressions:

df <- read.table(header=T, stringsAsFactors=F, text="
DATE PRCP
19490101   25
19490102    5
19490118   18
19490119  386
19490202   38")
dates <- as.character(df$DATE)
res <- t(sapply(regmatches(dates, regexec("(\\d{4})(\\d{2})(\\d{2})", dates)), "[", -1))
res <- structure(as.integer(res), .Dim=dim(res)) # make them integer values
cbind(df, setNames(as.data.frame(res), c("Y", "M", "D"))) # combine with original data frame
#       DATE PRCP    Y  M  D
# 1 19490101   25 1949 01 01
# 2 19490102    5 1949 01 02
# 3 19490118   18 1949 01 18
# 4 19490119  386 1949 01 19
# 5 19490202   38 1949 02 02