Recursive calcs on timeseries

Hi Martin,

Could you please turn this into a self-contained reprex (short for minimal reproducible example)? I see you have some example code in the StackOverflow question, but it will still help us help you if we can be sure we're all working with/looking at the same stuff.

Right now the best way to install reprex is:

# install.packages("devtools")

If you've never heard of a reprex before, you might want to start by reading the help page. The reprex dos and don'ts are also useful.

For pointers specific to the community site, check out the reprex FAQ, linked to below.