R change quarter to timestamp

Question

Hey I have some data aggregated at quarter level and there is a column contains data like this:

> unique(data$fiscalyearquarter)
 [1] "2012Q3" "2010Q3" "2012Q1" "2011Q4" "2012Q4" "2008Q1" "2008Q2" "2010Q4" "2010Q1"
[10] "2009Q2" "2012Q2" "2011Q3" "2013Q2" "2013Q1" "2011Q2" "2013Q4" "2009Q4" "2009Q3"
[19] "2011Q1" "2010Q2" "2013Q3" "2008Q4" "2009Q1" "2014Q1" "2008Q3" "2014Q2"

I am thinking about writing a function that turn a string into a timestamp.

Something like this, split the the string to be year and quarter and then force the quarter to be converted to be month(the middle of the quarter).

convert <- function(myinput = "2008Q2"){
  year <- substr(myinput, 1, 4)
  quarter <- substr(myinput, 6, 6)
  month <- 3 * as.numeric(quarter) - 1
  date <- as.Date(paste0(year, sprintf("%02d", month), '01'), '%Y%m%d')
  return(date)
}

I have to convert those strings to date format and then analyze it from there.

> convert("2010Q3")    
[1] "2010-08-01"

Is there any way beyond my hard coding solution to analyze time series problem at quarterly level?

Is it important to have the date be the second month in the quarter instead of the first? — GSee, Jan 12 '15 at 20:34
@GSee, you could modify you solution to something like that `temp <- as.POSIXlt(as.yearqtr(x)); temp$mon <- temp$mon + 1; as.Date(temp)` — David Arenburg, Jan 12 '15 at 20:42
@DavidArenburg yes, we could add a month, but it's a bad idea to modify POSIXlt objects like that — GSee, Jan 12 '15 at 20:43
@DavidArenburg This came up again recently here: http://stackoverflow.com/a/27841106/967840. For those without 10k rep, see [here](http://stackoverflow.com/questions/27841014/how-to-subtract-a-number-of-days-from-a-date-time), [here](http://stackoverflow.com/questions/25603995/no-weekday-shift-when-adding-hours-to-posixlt), and [here](http://stackoverflow.com/questions/14843439/problems-adding-a-month-to-x-using-posixlt-in-r-need-to-reset-value-using-as-d) — GSee, Jan 12 '15 at 20:46
@DavidArenburg nothing wrong with it being closed. I was referring to the deleted Answer when I mentioned the 10k requirement. — GSee, Jan 12 '15 at 20:51

GSee · Answer 1 · 2015-01-12T20:42:11.920

4

If x is your vector and you're okay having the date be the first day of the quarter:

library(zoo)
as.Date(as.yearqtr(x))

If you want the date to be the first day of the second month of the quarter like your example, you could hack together something like this:

as.Date(format(as.Date(as.yearqtr(x))+40, "%Y-%m-01"))

edited Jan 12 '15 at 20:42

answered Jan 12 '15 at 20:29

GSee

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Yo could also add something like `library(lubridate) ; temp <- as.POSIXct(as.yearqtr(x)) ; as.Date(temp + months(1))` I guess – David Arenburg Jan 12 '15 at 20:57

R change quarter to timestamp

1 Answers1