Improve grouping with groupRows. closes #294

[JanMarvin]

allow different grouping options for groupRows(). Needs testing due possible breaking changes to write_file_2.cpp.

[JanMarvin]

If this passes the checks (did not check prio to pushing) this needs some testing. I have made changes to the write function and got mad and did not try to fully understand the old code. Also I was not entirely sure how to handle grouping, because I do not really use it and therefore might have implemented changes that are unwanted/unneeded. Checked basic functionality with LO and MS 365.

[codecov-commenter]

Codecov Report

Merging #297 (50eac9f) into master (1c0295d) will increase coverage by 0.01%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #297      +/-   ##
==========================================
+ Coverage   66.48%   66.49%   +0.01%     
==========================================
  Files          34       34              
  Lines        8939     8942       +3     
==========================================
+ Hits         5943     5946       +3     
  Misses       2996     2996              

Impacted Files	Coverage Δ
src/write_file_2.cpp	0.00% <0.00%> (ø)
R/wrappers.R	52.24% <100.00%> (+0.09%)	⬆️

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[bfreed3]

I figured out what I needed to with the old groupRows function. For the iris df, to group on the first instance of each Species in the xlsx file, the following code works for what I need.

groupRows(wb, sheet=1, c(2:51,53:101,103:151))

One just needs to play around with it a bit, and understand the shifting of rows going from the df to xlsx, and how Excel groups things on its side.

Thanks, Burgess

[JanMarvin]

Thanks for the follow up. I kinda figured the same when creating this pull request. You can't have different grouped rows in the same outline that are attached to each other. Excel will automatically combine both. To avoid this, you need to skip at least one row. Though this pull request allows having multiple nested groups and it fixes the previous warning message.
If you want, you could add a pull request to further improve the documentation. Which is quite short for this function and lead to the issue.

[JanMarvin]

darn, I got lost with open pull requests (293 != 294) anyone got a copy of this branch lying around? 😄
Edit: fixed and restored. git reflog ftw!