Automatic assignment of references to bibliography categories depending on origdate or date

Question

I'm using biblatex-chicago with the author-date option. I love biblatex and biblatex-chicago and appreciate the work that has been put into it. I have a small question, however. I usually divide my bibliography into sections using

\DeclareBibliographyCategory{A}

in the preamble and then

\autocite{B}

\AddToCategory{A}{B}

following a citation of B.

Now I wonder, if it's possible to have a bibliography category:

\DeclareBibliographyCategory{Before1900}

and have a reference be added automatically to the category Before1900 if:

1. It has an origdate value and that value is lower than 1900;
2. It has no origdate value but the date value is lower than 1900.

I would be interested in such an option since it would enable me to automatically create a split bibliography according to the date a source was written/published.

Answer 1

biblatex allows us to filter the entries to be inserted in a bibliography.

First of all you have to define the conditions to be used using \definebibcheck

\defbibcheck{pre}{
  \iffieldint{origyear}
    {\ifnumless{\thefield{origyear}}{1900}
      {}
      {\skipentry}
    }
    {\iffieldint{year}
      {\ifnumless{\thefield{year}}{1900}
        {}
        {\skipentry}
      }
      {\skipentry}
    }
}

\defbibcheck{post}{
  \iffieldint{origyear}
    {\ifnumless{1899}{\thefield{origyear}}
      {}
      {\skipentry}
    }
    {\iffieldint{year}
      {\ifnumless{1899}{\thefield{year}}
        {}
        {\skipentry}
      }
      {
       \skipentry %comment out this line if unknown date check used as well.
      } 
    }
}

after that you can use the checks in a \printbibliography command

\printbibliography[check=pre,title={Before 1900}]

\printbibliography[chek=post,title={Post 1900}]

EDIT

To create a third class of entries, those with unclear dating, the check could be as follows:

\defbibcheck{dateunknown}{
  \ifboolexpr{
    test {\iffieldundef{year}}
    and
    test {\iffieldundef{origyear}}
  }
    {}
    {\skipentry}
}