How to flag last friday or last day or month

Question

I have a data frame of dates and the day of the week

> head(data)
         day   weekday
1 2016-01-01    Friday
4 2016-01-04    Monday
5 2016-01-05   Tuesday
         


        

Answer 1

require(data.table)

lfom<-function(d){
  x<-seq(min(d),max(d),by=1)
  fri<-which(wday(x)==6)
  mend<-which(mday(x)==1)-1
  d %in%  x[fri[findInterval(mend,fri)]]
}

ldom<-function(d){
  x<-seq(min(d),max(d),by=1)
  mend<-which(mday(x)==1)-1
  d %in%  x[mend]
}


data <-data.frame(
  day = seq(as.Date("2014-01-01"), as.Date("2016-05-10"), "day"), 
  weekday = weekdays(seq(as.Date("2014-01-01"), as.Date("2016-05-10"), "day"))
)
excludeDays <- c("Saturday", "Sunday")
data <- data.table(subset(data, !weekdays(data$day) %in% excludeDays)) #exclude weekend
data$lfom<-lfom(data$day)
data$ldom<-ldom(data$day)