Bucketing data into weekly, bi-weekly, monthly and quarterly data in R

Question

I have a data frame with two columns. Date, Gender

I want to change the Date column to the start of the week for that observation. For example if Jun-28-2011 is a Tuesday, I'd like to change it to Jun-27-2011. Basically I want to re-label Date fields such that two data points that are in the same week have the same Date.

I also want to be able to do it by-weekly, or monthly and specially quarterly.

Update: Let's use this as a dataset.

datset <- data.frame(date = as.Date("2011-06-28")+c(1:100))

Answer 1

One slick way to do this that I just learned recently is to use the lubridate package:

library(lubridate)
datset <- data.frame(date = as.Date("2011-06-28")+c(1:100))
#Add 1, since floor_date appears to round down to Sundays
floor_date(datset$date,"week") + 1

I'm not sure about how to do bi-weekly binning, but monthly and quarterly are easily handled with the respective base functions:

quarters(datset$date)
months(datset$date)

EDIT: Interestingly, floor_date from lubridate does not appear to be able to round down to the nearest quarter, but the function of the same name in ggplot2 does.

Answer 2

Look at ?strftime. In particular, the following formats:

%b: Abbreviated month name in the current locale. (Also matches full name on input.)

%B: Full month name in the current locale. (Also matches abbreviated name on input.)

%m: Month as decimal number (01–12).

%W: Week of the year as decimal number (00–53) using Monday as the first day of week (and typically with the first Monday of the year as day 1 of week 1). The UK convention.

eg:

> strftime("2011-07-28","Month: %B, Week: %W")
[1] "Month: July, Week: 30"

> paste("Quarter:",ceiling(as.integer(strftime("2011-07-28","%m"))/3))
[1] "Quarter: 3"