Format date as Year/Quarter

Question

I have the following dataframe:

Data <- data.frame(   date = c("2001-01-01", "2001-02-01", "2001-03-01", "2001-04-01", "2001-05-01", "2001-06-01"),   qtr = c("NA", "NA","NA","NA","NA","NA") ) 

I want to fill Data$qtr with Year/Quater - f.e. 01/01 (I need this format!).

I wrote a function:

fun <- function(x) {    if(x == "2001-01-01" | x == "2001-02-01" | x == "2001-03-01") y <- "01/01"   if(x == "2001-04-01" | x == "2001-05-01" | x == "2001-06-01") y <- "01/02"   return(y) } n$qtr <- sapply(n$date, fun) 

But it does not work. I always get the error message:

Error in FUN(X[[1L]], ...) : Object 'y' not found 

Why?

Answer 1

You need to explicilty Vectorize your function:

fun_v <- Vectorize(fun, "x") fun_v(Data$date) #[1] "01/01" "01/01" "01/01" "01/02" "01/02" "01/02" 

However, when it comes to more or less standard tasks (such as datetime manipulations), there's always a solution already available:

library(zoo) yq <- as.yearqtr(Data$date, format = "%Y-%m-%d") yq #[1] "2001 Q1" "2001 Q1" "2001 Q1" "2001 Q2" "2001 Q2" "2001 Q2" 

To convert to your specific format, use

format(yq, format = "%y/0%q") #[1] "01/01" "01/01" "01/01" "01/02" "01/02" "01/02" 

Answer 2

I have been loving the lubridate package for working with dates. Super slick. The quarter function finds the quarter (of course) and then just pair that with the year.

library(lubridate) Data <- Data %>%   mutate(qtr = paste0(substring(year(date),3,4),"/0",quarter(date)))  

If you are not familiar with the %>% from magrittr the first line basically says "use data frame called Data" and the second line says "mutate (or add) a column called qtr"

EDIT 2021-Q2

If the "YY/QQ" format is not critical, then a quick and safe way to get the year and the quarter is:

library(lubridate) Data %>%   mutate(qtr = quarter(date, with_year = T))