Copying keywords from one BibTeX field to another using DeclareSourcemap doesn't work

Question

My BibTeX entries have a keywords field with keywords describing the content. I also have a field called tags with meta information like talk, manuscript, own, etc. Example:

@inproceedings{MalsburgVasishth2007ECEM,
  author = {von der Malsburg, Titus and Vasishth, Shravan},
  title = {A Time-Sensitive Similarity Measure for Scanpaths},
  crossref = {ECEM2007},
  keywords = {eyetracking, scanpaths, method},
  tags = {poster, own}
}

Using printbibliography, I can filter entries with certain keywords

`\printbibliography[keyword=eyetracking]

but I also want to filer entries with certain tags. For example, I'd like to have a section in my CV that lists my posters. How can I achieve this?

I suppose one solution would be to append the content of the tags field to the keywords field using a DeclareSourcemap contraption. Such a solution was given before but it doesn't work as expected. Here is a MWE:

\RequirePackage{filecontents}
\begin{filecontents*}{bibliography.bib}
@article{MalsburgEtAl2014,
  author = {von der Malsburg, Titus and Kliegl, Reinhold and Vasishth, Shravan},
  title = {Determinants of Scanpath Regularity in Reading},
  journal = {Cognitive Science},
  year = {2014},
  keywords = {eyemovements, method, parsing, scanpaths, corpus},
  tags = {article, own}
}
\end{filecontents*}

\documentclass{article}
\usepackage[backend=biber]{biblatex}
\DeclareLanguageMapping{american}{american-apa}
\addbibresource{bibliography.bib}
\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
       \step[fieldsource=tags, fieldtarget=keywords]
    }
  }
}

\begin{document}
\section{Publications}
\nocite{MalsburgEtAl2014}
\printbibliography[keyword=article,notkeyword=submitted,keyword=own,heading=none]
\end{document}

When I compile this, I get the following error messages:

Package biblatex Warning: Keyword 'article' not found on input line 34.
Package biblatex Warning: Keyword 'own' not found on input line 34.
LaTeX Warning: Empty bibliography on input line 34.

Also, the reference is not shown in the PDF.

Answer 1

(This is a revised solution. Thanks to @moewe for pointing out how to simplify it.)

Basically, what you want to do is copy your tags field to the keywords field, but after also adding a comma so the final keyword is not run together with the first word from the tags field.

\RequirePackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{MalsburgEtAl2014,
  author = {von der Malsburg, Titus and Kliegl, Reinhold and Vasishth, Shravan},
  title = {Determinants of Scanpath Regularity in Reading},
  journal = {Cognitive Science},
  year = {2014},
  keywords = {eyemovements, method, parsing, scanpaths, corpus},
  tags = {article, own},
}
\end{filecontents*}

\documentclass{article}
\usepackage[backend=biber]{biblatex}
\DeclareLanguageMapping{american}{american-apa}
\addbibresource{\jobname.bib}
\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite]{
       \step[fieldsource=tags,]
       \step[fieldset=keywords, fieldvalue={,}, append]
       \step[fieldset=keywords, origfieldval, append]
    }
  }
}

\begin{document}
\section{Publications}
\nocite{MalsburgEtAl2014}
\printbibliography[keyword=article, notkeyword=submitted, keyword=own,
heading=none]
\end{document}

Note that Biber and BibTeX will ignore fields they don't recognize. So your tags field is copied, but subsequently 'lost'. (You can 'save' it with a judicious use of the \DeclareDatamodelFields command, but it is not needed for this application.)