Read csv as stanfit v2 (alternative version)

[venpopov]

An alternative version of #1618, as I noted in my comment here

Rather than having a new function, here I slightly modify the existing read_csv_as_stanfit() function and export it instead. I find this option a bit cleaner, slightly faster and likely easier to maintain.

• combines read_csv_as_stanfit and read_csv_as_brms_stanfit into one function
• eliminates redundant reading metadata from file
• remove redundant renaming
• remove renaming samples columns that otherwise needs to be fixed (displaying models fitted pre 2.16 in brms 2.16 - variables missing in the draws object #1218)

The main things to note

• previously there was a separate read_cmdstan_csv() call that only reads in the metadata. This is unnecessary, since all of that information is already contained in the call to read_cmdstan_csv() in read_csv_as_stanfit(). This speeds up the import by ~10-20% in my testing.
• I removed these lines:

  colnames(samples) <- gsub("\\[", ".", colnames(samples))
  colnames(samples) <- gsub("\\]", "", colnames(samples))
  colnames(samples) <- gsub("\\,", ".", colnames(samples))

as they introduce the issue that then needs to be solved by repair_stanfit()

Feel free to go with either #1618 or this.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 19 lines in your changes are missing coverage. Please review.

Project coverage is 82.10%. Comparing base (15c0754) to head (0919664).
Report is 1 commits behind head on master.

❗ Current head 0919664 differs from pull request most recent head b8fd782. Consider uploading reports for the commit b8fd782 to get more accurate results

Files	Patch %	Lines
R/backends.R	0.00%	19 Missing ⚠️

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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1619   +/-   ##
=======================================
  Coverage   82.09%   82.10%           
=======================================
  Files          70       70           
  Lines       19849    19847    -2     
=======================================
  Hits        16295    16295           
+ Misses       3554     3552    -2     

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[paul-buerkner]

Looks good, thank you! I made some minor edits and will now merge the PR.

[venpopov]

Cool, thank you, this will be super useful for me! And thanks for adding me as a contributor.