Customizing citations depending on the author with BibLaTeX style "authoryear" or "authoryear-comp"

Question

Say I use BibLaTeX with standard style authoryear or authoryear-comp.

Then given a citation command such as \parencite{A, B, C} (or any other standard Biblatex citation command), I'd like the resulting citations to be typeset differently depending on whether a given field (e.g. the author field) in the corresponding bibliography entry contains a given string (e.g. someone's lastname).

MWE:

\documentclass{article}
\usepackage{filecontents}
\usepackage[backend=biber,style = authoryear-comp]{biblatex}
\usepackage[colorlinks=true, breaklinks, allcolors = blue]{hyperref}
\DeclareSourcemap{%
  \maps[datatype=bibtex]{%
    \map{%
      \step[fieldsource=author, match=Doe, final]%
      \step[fieldset=keywords, fieldvalue=doe]%
    }%
  }%
}
\begin{filecontents}{\jobname.bib}
@Book{p1,
  author =       "A. U. Thor and John Doe",
  title =        "A Scientific Article 1",
  year =         "1975"  
}
@Book{p2,
  author =       "John Doe",
  title =        "A Scientific Article 2",
  year =         "1985"  
}
@Book{p3,
  author =       "Joe Bar",
  title =        "A Scientific Article 3",
  year =         "1995"  
}
@Book{p4,
  author =       "Jane Baz",
  title =        "A Scientific Article 4",
  year =         "2005"  
}
@Book{p5,
  author =       "A. U. Thor and John Doe",
  title =        "A Scientific Article 5",
  year =         "2010"  
}
@Book{p6,
  author =       "Jane Baz",
  title =        "A Scientific Article 6",
  year =         "2015"  
}
\end{filecontents}
\addbibresource{\jobname.bib}

\nocite{*}
\begin{document}
In: \parencite{p4, p1, p2, p3, p5, p6}, ``Thor and Doe 1975, 2010'' and ``Doe
1985'' should be \emph{emphasized} (but the corresponding entries in the
References section should remain typeset as the others).

\printbibliography
\end{document}

Note: I asked a similar question here but the proposed solution does not work with standard styles authoryear or authoryear-comp.

Answer 1

If you want this to be applicable to multiple styles, we can modify the cite bibmacro as follows

\DeclareFieldFormat{keywordcite}{\ifkeyword{doe}{\mkbibemph{#1}}{#1}}
\csletcs{old:cite}{abx@macro@cite}
\renewbibmacro{cite}{\printtext[keywordcite]{\csuse{old:cite}}}

MWE

\documentclass{article}
\usepackage{filecontents}
\usepackage[backend=biber,style = authoryear-comp]{biblatex}
\usepackage[colorlinks=true, breaklinks, allcolors = blue]{hyperref}
\DeclareSourcemap{%
  \maps[datatype=bibtex]{%
    \map{%
      \step[fieldsource=author, match=Doe, final]%
      \step[fieldset=keywords, fieldvalue=doe]%
    }%
  }%
}
\begin{filecontents}{\jobname.bib}
@Book{p1,
  author =       "A. U. Thor and John Doe",
  title =        "A Scientific Article 1",
  year =         "1975"  
}
@Book{p2,
  author =       "John Doe",
  title =        "A Scientific Article 2",
  year =         "1985"  
}
@Book{p3,
  author =       "Joe Bar",
  title =        "A Scientific Article 3",
  year =         "1995"  
}
@Book{p4,
  author =       "Jane Baz",
  title =        "A Scientific Article 4",
  year =         "2005"  
}
@Book{p5,
  author =       "A. U. Thor and John Doe",
  title =        "A Scientific Article 5",
  year =         "2010"  
}
@Book{p6,
  author =       "Jane Baz",
  title =        "A Scientific Article 6",
  year =         "2015"  
}
\end{filecontents}
\addbibresource{\jobname.bib}

\DeclareFieldFormat{keywordcite}{\ifkeyword{doe}{\mkbibemph{#1}}{#1}}
\csletcs{old:cite}{abx@macro@cite}
\renewbibmacro{cite}{\printtext[keywordcite]{\csuse{old:cite}}}

\nocite{*}
\begin{document}
In: \parencite{p4, p1, p2, p3, p5, p6}, ``Thor and Doe 1975, 2010'' and ``Doe
1985'' should be \emph{emphasized} (but the corresponding entries in the
References section should remain typeset as the others).

\printbibliography
\end{document}