Use custom field and count elements of lists in references using biblatex/biber

Question

I have a primary source and analyzed its references (on which pages are the references cited, like a manual backref job). I created a new library for this (like the author would to if he had LaTeX a few centuries ago) and added a custom field citedonpages with the manually discovered pages.

I would like to print this analyzed data (e.g. for displaying it in a table). Is it possible to use biblatex/biber to process additional fields (in this case citedonpages as described in citedonpages.dbx) to

• print this list for each entry
• and count the comma separated entries?

I tried to follow https://tex.stackexchange.com/a/163396/4419 but the command \printfield{citedonpages} did non work.

How can I access (print) the citedonpages field and how can I count the entries of the comma-separated values? As the real library has many entries, an automated solution would be very helpful (and ideally completely within LaTeX).

MWE (as a follow-up question of Create table from references with custom fields as columns using biblatex/biber):

\documentclass{scrbook}

\begin{filecontents*}{citedonpages.dbx}
    \ProvidesFile{citedonpages.dbx}[2021/07/27 add citedonpages field to biblatex data model]
    \DeclareDatamodelFields[type=field,datatype=literal]{citedonpages} %comma seperated list of values
    \DeclareDatamodelEntryfields{citedonpages}
\end{filecontents*}

\begin{filecontents*}{Analysis.bib}
@Book{Miller1832a,
    author    = {John Miller},
    title     = {Elementary book},
    year      = {1832},
    citedonpages = {67,68,97},
}

@InBook{Smith1744a,
    author    = {Daniel Smith},
    booktitle = {Collection of important articles},
    location  = {Amsterdam},
    title     = {Noteworthy Article},
    year      = {1744},  
    citedonpages = {5, 23, 37, 79, 248, 249, 254},
}
\end{filecontents*}
%\addbibresource{Analysis.bib}

\usepackage{longtable,array}
\usepackage{booktabs,lipsum,tabularx}
\usepackage[backend=biber,datamodel=citedonpages,style=authortitle]{biblatex}
\usepackage{biblatex-ext-tabular}

\DeclareFieldFormat{citedonpages}{\bibstring{citedonpages}\space #1}
    
\defbibtabular{bibtabular}
  {\renewbibmacro*{bbx:dashcheck}[2]{##2}%
   \begin{longtable}{@{}llccl@{}}
     \toprule
     \textbf{Author} & \textbf{Title} & \textbf{Year} & \textbf{\# Citations} & \dots\ on pages\\
     \midrule}
  {\bottomrule
   \end{longtable}}
  {\anchorlang{\usebibmacro{author/editor+others}}
   & \plainlang{\usebibmacro{title}}
   & \plainlang{\printdate}
   & 0 % how to display counter
   & \printfield{citedonpages}
   \\}


\begin{document}

\begin{refsection}[Analysis.bib]
\nocite{*}
\printbibliography[heading=none]
\end{refsection}

\textbf{Ideally, it should output something like:}\\
Miller, John. \textit{Elementary book}. 1832. (cited 3 times on pages 67, 68, 97)\\
Smith, Daniel. “Noteworthy Article”. In: \textit{Collection of important articles}. Amsterdam,
1744. (cited 7 times on pages 5, 23, 37, 79, 248, 249, 254)

\vspace{1cm}\textbf{Version with table} (added manually):

\begin{tabularx}{0.95\textwidth}{llccX}
        \toprule 
        {\bfseries Author} & {\bfseries Title}  & {\bfseries Year} & {\bfseries \#  Citations}  & ... on pages \\\midrule%\otoprule 
                Miller, John       & Elementary book    & 1832             & 3 & 67, 68, 97\\
        Smith, Daniel      & "Noteworthy article" & 1744           & 7 & 5, 23, 37, 79, 248, 249, 254 \\
        \bottomrule
\end{tabularx}

\vspace{1cm}\textbf{Version with table} (autogenerated, but entries are missing):

\begin{refsection}[Analysis.bib]
\nocite{*}
\printbibtabular[heading=none]
\end{refsection}

\end{document}

Answer 1

We can use expl3 code to read the list of pages, remove duplicate numbers and count the number of pages.

This can be done in \DeclareFieldInputHandler, so happens right when the field citedonpages is read from the .bbl file. From the on, citedonpages contains a nicely formatted list of pages (without duplication).

The remaining code can be taken almost verbose from Create table from references with custom fields as columns using biblatex/biber, we just need to print our citedonpages field instead of the biblatex pageref list.

\documentclass[british]{article}
\usepackage[T1]{fontenc}
\usepackage{babel}
\usepackage{csquotes}

\begin{filecontents*}{citedonpages.dbx}
\ProvidesFile{citedonpages.dbx}[2021/07/27 add citedonpages field to biblatex data model]
\DeclareDatamodelFields[type=field, datatype=literal]{citedonpages}
\DeclareDatamodelEntryfields{citedonpages}
\end{filecontents*}

\usepackage[backend=biber, style=authoryear, datamodel=citedonpages]{biblatex}
\usepackage{biblatex-ext-tabular}

\makeatletter
\ExplSyntaxOn
\clist_new:N \l__kromuchiblx_citedonpages_clist

\DeclareFieldInputHandler{citedonpages}
  {
    \clist_set:Nn \l__kromuchiblx_citedonpages_clist {#1}
    % remove duplicates, if you want the duplicates counted,
    % move this line *after* the citecount definition
    \clist_remove_duplicates:N \l__kromuchiblx_citedonpages_clist
    % writing a new field *while* we are processing another
    % is a bit risky, ...
    \blx@bbl@fieldedef{citecount}{\clist_count:N \l__kromuchiblx_citedonpages_clist}
    % ... but works if we make sure *we* write \NewValue
    \edef\NewValue{\clist_use:Nn \l__kromuchiblx_citedonpages_clist {,~}}
  }
\ExplSyntaxOff
\makeatother

\usepackage{longtable}
\usepackage{array}
\usepackage{booktabs}

\newcolumntype{L}[1]{%
  >{\raggedright\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}
\newcolumntype{C}[1]{%
  >{\centering\let\newline\\\arraybackslash\hspace{0pt}}p{#1}}

\newbibmacro*{tablepageref}{%
  \printfield{citedonpages}}

\renewbibmacro*{pageref}{}

\defbibtabular{bibtabular}
  {\renewbibmacro*{bbx:dashcheck}[2]{##2}%
   \renewbibmacro*{labeltitle}{}%
   \renewbibmacro*{date+extradate}{}%
   \setlength{\LTpre}{0pt}%
   \setlength{\LTpost}{0pt}%
   \renewcommand*{\arraystretch}{2}%
   \begin{longtable}{%
                     @{}
                     L{\dimexpr0.2\textwidth-1\tabcolsep\relax}
                     L{\dimexpr0.25\textwidth-2\tabcolsep\relax}
                     L{\dimexpr0.12\textwidth-2\tabcolsep\relax}
                     L{\dimexpr0.22\textwidth-2\tabcolsep\relax}
                     L{\dimexpr0.21\textwidth-1\tabcolsep\relax}
                     @{}}
     \toprule
     \textbf{Author} & \textbf{Title} & \textbf{Year} & \textbf{\# Citations} & \dots\ on pages\\
     \midrule}
  {\bottomrule
   \end{longtable}}
  {\anchorlang{\usebibmacro{author/editor+others}}
   & \plainlang{\usebibmacro{title}}
   & \plainlang{\printdate}
   & \plainlang{\printfield{citecount}} 
   & \plainlang{\usebibmacro{tablepageref}} \\}

\begin{filecontents*}{\jobname.bib}
@Book{Miller1832a,
  author       = {John Miller},
  title        = {Elementary book},
  year         = {1832},
  citedonpages = {67,67,68,97,67},
}
@inbook{Smith1744a,
  author       = {Daniel Smith},
  booktitle    = {Collection of important articles},
  location     = {Amsterdam},
  title        = {Noteworthy Article},
  year         = {1744},  
  citedonpages = {5, 23, 37, 79, 248, 249, 254},
}
\end{filecontents*}
\addbibresource{\jobname.bib}

\begin{document}
\nocite{*}
\printbibtabular[title=Analysis]
\end{document}