BibLaTeX: Remapping groups field as keywords field doesn't work

Question

I want to use the groups from my literature management tool as keywords for BibLaTeX to create specific bibliographies for certain chapters. I managed to remap the groups field as a keywords field if an entry contains both fields, however, this seems not to work. How do I have to adjust the \DeclareSourcemap command to make this work? Thanks in advance!

MWE:

\documentclass[a4paper,12pt]{scrartcl}

  \usepackage{filecontents}
  \usepackage[
    backend=biber,
    style=authoryear-comp,
  ]{biblatex}

  \DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
       \step[fieldsource=groups, fieldtarget=keywords]
    }
  }
}

\begin{filecontents}{sample.bib}
  @article{greenwade93,
    author  = "George D. Greenwade",
    title   = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
    year    = "1993",
    journal = "TUGBoat",
    volume  = "14",
    number  = "3",
    pages   = "342--351",
    keywords  = {bar},
    groups  = {foo}
}

  @article{redwade93,
    author  = "George D. Redwade",
    title   = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
    year    = "1993",
    journal = "TUGBoat",
    volume  = "14",
    number  = "3",
    pages   = "342--351",
    groups  = {foo}
}

  @article{bluewade93,
    author  = "George D. Bluewade",
    title   = "The {C}omprehensive {T}ex {A}rchive {N}etwork ({CTAN})",
    year    = "1993",
    journal = "TUGBoat",
    volume  = "14",
    number  = "3",
    pages   = "342--351",
    keywords  = {bar}
}
\end{filecontents}

  \addbibresource{sample.bib}

\begin{document}

This document contains citations of \cite{greenwade93}, \cite{redwade93} and \cite{bluewade93}---but \cite{greenwade93} doesn't appear in the first bibliography.

\printbibliography[keyword=foo,title={Bibliography One}]

\printbibliography[keyword=bar,title={Bibliography Two}]

\end{document}

Answer 1

By default, biblatex is very reluctant to change or overwrite existing fields. You will have to encourage it with overwrite=true.

Up to and including version 2.7 of Biber the fieldtarget approach seems to have trouble with existing fields even if overwrite=true us enabled, however. You could use

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite=true]{
       \step[fieldsource=groups]
       \step[fieldset=keywords, origfieldval]
    }
  }
}

This will simply overwrite keywords with the content of groups.

This problem is fixed in version 2.8 (DEV version, not yet released), so we can then use

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite=true]{
       \step[fieldsource=groups, fieldtarget=keywords]
    }
  }
}

If you want to collect both fields into keywords use

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite=true]{
       \step[fieldsource=keywords, final]
       \step[fieldsource=groups]
       \step[fieldset=keywords, fieldvalue={,}, append]
       \step[fieldset=keywords, origfieldval, append]
    }
    \map{
       \step[fieldsource=groups]
       \step[fieldset=keywords, origfieldval]
    }
  }
}

With this groups is copied to keywords if the latter does not exist; the contents of groups is appended to keywords if there already are some keywords present (note that we need to insert a comma, so we can't do both steps in one go).