Write sst with inline_string = FALSE

[JanMarvin]

closes #67

what is this about?

Currently we write every character as inlineStr. Therefore we have a couple of cells like this

<c t="inlineStr">
 <is>
   <t>foo</t>
 </is>
</c>

This is completely fine with the open xml standard. But Excel usually writes characters as sharedStrings. They provide a sharedStrings.xml file looking like this:

<sst uniqueCount="1">
  <si>
    <t>foo</t>
  </si>
</sst>

and a cell that looks like this:

<c t="s">
  <v>0</v>
</c>

update

I have decided to go a different route. For now we treat sharedStrings similar to inlineStrings and simply create the shared strings once we are done with adding data.

• write strings as <is><t>...</t></is> to cc
• check for unique strings in cc
• combine these with wb$sharedStrings
• replace cc values with index positions
• update cc and wb$shareStrings

This brings the benefit of having shared strings over the workbook which can reduce the overall file size with string duplicates in a workbook. But, since we do not check for these initially, it is a bit slower, because of the unique and match calls once writing is done. On the other side it brings the benefit of potentially smaller files and the code is a lot cleaner.

library(openxlsx2)

res <- microbenchmark::microbenchmark(
  wb_workbook()$add_worksheet()$add_data(x = iris, inline_strings = FALSE),
  wb_workbook()$add_worksheet()$add_data(x = iris, inline_strings = TRUE),
  times = 100
); res
#> Unit: milliseconds
#>                                                                      expr
#>  wb_workbook()$add_worksheet()$add_data(x = iris, inline_strings = FALSE)
#>   wb_workbook()$add_worksheet()$add_data(x = iris, inline_strings = TRUE)
#>       min       lq     mean   median       uq       max neval
#>  5.419856 5.581581 6.763844 5.901882 6.227162 54.860594   100
#>  5.115616 5.287041 5.785157 5.533161 5.982857  9.783031   100