R Time periods overlapping

Question

Using the lubridate library, I can find out if two time periods overlapped. But, is there an efficient way to compute for how many days they overlapped. (for instance how many days a women smoked while pregnant. The pregnancy period and smoking period may overlap totally, partially or not at all)

Here is an example with three women:

preg_start<-as.Date(c("2011-01-01","2012-01-01","2013-01-01"))
preg_end<-preg_start+270 # end after 9 months
smoke_start<-as.Date(c("2011-02-01","2012-08-01","2014-01-01"))
smoke_end<-smoke_start+100 # all three smoked 100 days

data<-data.frame(cbind(preg_start,preg_end,smoke_start,smoke_end))

I want to add a variable saying that the first woman smoked 100 days during pregnancy, the second smoked 30 days and the third did not smoke while pregnant.

Answer 1

Use interval to create time intervals for pregnancy and smoking. Then calculate the intersect of these intervals. From that you can calculate the period in days.

library("lubridate")
preg_start<-as.Date(c("2011-01-01","2012-01-01","2013-01-01"))
preg_end<-preg_start+270 # end after 9 months
smoke_start<-as.Date(c("2011-02-01","2012-08-01","2014-01-01"))
smoke_end<-smoke_start+100 # all three smoked 100 days

smoke <- new_interval(smoke_start, smoke_end, tzone="UTC")
preg <- new_interval(preg_start, preg_end, tzone="UTC")
day(as.period(intersect(smoke, preg), "days"))

I get 100, 57 and 0 days of smoking during pregnancy.