R how to get sixth workday of the month

Question

I have a vector of business dates:

require(bizdays)
cal <- create.calendar(name='MyCalendar', weekdays=c('sunday', 'saturday'))
startdate = as.Date(Sys.Date()) %m-% years(5) # today minus 5yrs
enddate = as.Date(Sys.Date())
dates = bizseq(startdate,enddate, cal)

Now I want to extract every 6th workday of very month from the dates vector, any ideas how to do this?

Thanks,

Jelle

Answer 1

You're really just looking to get every 6th value of the vector by group of month and year. We can use base ave() with lubridate to get what you want:

library(bizdays)
library(lubridate)

m_days <- ave(1:length(dates), month(dates), year(dates), FUN = seq_along)
result <- dates[m_days %% 6 == 0]
head(result)
#> [1] "2015-08-28" "2015-09-08" "2015-09-16" "2015-09-24" "2015-10-08"
#> [6] "2015-10-16"