Create beginning of date ranges with a varying number of days-CodePudding

I have a data frame with a list of enddates of fiscal quarters between 2014 and 2021. I want to create a separate column with the beginning of each of these quarters. Note that the format is YYYY-MM-DD. It looks like this:

df <- data.frame(end = c("2014-12-31", "2015-03-31","2015-06-30", "2015-09-30", "2015-12-31", "2016-03-31"))

The dates quarters are always from

Jan 1st to Mar 31st
Apr 1st to Jun 30th
Jul 1st to Sep 30th
Oct 1st to Dec 31st

My current code works by creating a separate column for each date with an ifelse statement and then adding them all together like this:

hmd$dtime_2 <- ifelse(hmd$dtime == "2015-03-31","2014-01-01", "")
hmd$dtime_3 <- ifelse(hmd$dtime == "2015-06-30", "2015-04-01", "")
hmd$dtime_4 <- ifelse(hmd$dtime == "2015-09-30","2015-07-01", "")
hmd$dtime_5 <- ifelse(hmd$dtime == "2015-12-31", "2015-10-01", "")

I know that there has to be an easier way to do this and I'd appreciate the help!

CodePudding user response：

This is made easily in lubridate. Get the first day of the month with floor_date and retracts two months to it with %m-% months(2). You then get the first date of the semester.

library(lubridate)
library(dplyr)
df %>% 
  mutate(start = floor_date(ymd(end), unit = "month") %m-% months(2))

         end      start
1 2014-12-31 2014-10-01
2 2015-03-31 2015-01-01
3 2015-06-30 2015-04-01
4 2015-09-30 2015-07-01
5 2015-12-31 2015-10-01
6 2016-03-31 2016-01-01

CodePudding user response：

You could use seq.Date.

sapply(df$end, \(x) as.character(seq.Date(as.Date(x)   1, by='-1 month', length.out=2)[2]))
# [1] "2014-12-01" "2015-03-01" "2015-06-01" "2015-09-01" "2015-12-01" "2016-03-01"

Data:

df <- structure(list(end = structure(c(16435, 16525, 16616, 16708, 
16800, 16891), class = "Date")), row.names = c(NA, -6L), class = "data.frame")