Q: fill up time gap when only start dates are available I have a data frame:
ColA <- c(1,1,1,2,2,3)
ColB <- c("a1","a1","a1","b2","c2","d3")
ColC <-as.Date(c("1999-02-01","2001-03-05","2010-01-01","2005-05-22","2008-07-24","2015-06-09"))
ColD <- c("high","low","middle","middle","high","high")
Questions <- data.frame(ColA,ColB,ColC,ColD)

Desired Output:
ColA ColB ColC        ColD
1    a1   1999-02-01  high
1    a1   1999-02-02  high
....
1    a1   2001-03-04  high
1    a1   2001-03-05  low
.....etc....... 

What I want to do is to derive and "fill up" the gapes between the Dates where input of other columns changes. So that e.g. ColA = 1 will be the same output in ColD as long as its not "2001-03-05". Ideally it should fill up in days. Any suggestion how to do it? Main issue is here, that ColA and ColB are like a foreign key to be handled. so when a value in either ColA or ColB changes, both need to be evaluated until the present time, while when only ColC or ColD changes, they need to stop where the next date starts. Hope I did explain it right.
Best Regards,
Christian
