Improve the calculation system in R-Instat?

[rdstern]

The two general innovations in R-Instat are the data book and the calculation system. We now have R packages on each. I list things we don't yet have in R-Instat, and wonder whether some, or all, could be considered as improvements in the calculation system.

a) We don't have working versions of the (logical) status variables for the start, end and length of the season. We are close and @lilyclements with @MeSophie have been working hard on them. But none are yet correctly implemented. They are exported to google buckets for e-picsa, so it would be good to get them working. I suggest help from @volloholic may be needed?
b) We have filters and selects as "data-type" objects stored in the data book. We don't yet have calculation objects. I think there was originally a plan by David and Danny that we could/should? If we do, then I wonder if we have 3 types of calculation, namely scalar, variable (or column) and summary? So it could produce a single value, or a column, or a summary in another data frame.
c) We export climatic definitions as one type of information to google buckets (with stations and summaries as the others). We have requested @lilyclements whether they could be less mysterious, and stored in the data book, like other objects. They seem to be like caclulations?
d) The calculations (at least the calculator) doesn't yet take any account of filters. Could it? @volloholic says that should be easy.
e) We have a general calculation dialog. It is now called Prepare > Data Reshape > General Summaries. I suggest its name be changed to General Calculation. I think it is now working, after improvements by @N-thony. But it lacks an Edit facility. Should that now be added, so the dialog could be used for the complex calculations that are needed, particularly in Climatic?
f) We don't yet cope with multiple missing values. @volloholic says they should be easy!