rnazoona.approx

Reverse/backward na.approx

I have a date vector with leading NAs and I'd like to generate an approximate sequence for these NAs using na.approx from package zoo.

na.approx does not work for leading NAs:

x <- as.Date(c(rep(NA,3),"1992-01-16","1992-04-16","1992-07-16",
"1992-10-16","1993-01-15","1993-04-16","1993-07-17"))
as.Date(na.approx(x,na.rm=FALSE))

[1] NA           NA           NA           "1992-01-16" "1992-04-16" 
1992-07-16" "1992-10-16" "1993-01-15" "1993-04-16" "1993-07-17"

I thought that I could reverse my vector using rev but I still get NAs

as.Date(na.approx(rev(x),na.rm=FALSE))

 [1] "1993-07-17" "1993-04-16" "1993-01-15" "1992-10-16" "1992-07-16" 
"1992-04-16" "1992-01-16" NA           NA           NA

Any ideas?

Solution

  • Found my answer. na.spline does a good job with lots of data. In the example above, I have few dates which causes the approximation to drift. However, in my real life example, there is no drift.

    as.Date(na.spline(x,na.rm=FALSE))
 [1] "1993-07-17" "1993-04-16" "1993-01-15" "1992-10-16" "1992-07-16" 
"1992-04-16" "1992-01-16" "1991-10-15" "1991-07-13" "1991-04-06"