How to extract year from date in iso 8601 format?

Question

I want to extract the year (or day or month) of a date which is stored as ISO 8601 in a database.

My MWE looks like:

\documentclass{article}
\usepackage{xstring}
\usepackage{datatool}
\newcommand{\myload}[3][1]{%
  \DTLgetvalue
  {\thevalue}
  {#2}
  {#1}
  {\dtlcolumnindex
    {#2}
    {#3}}%
}
%\get{<DATABASE>}{<FIELD>}
\newcommand{\get}[3][1]{%
  \myload[#1]{#2}{#3}
   \thevalue%
  }
% https://tex.stackexchange.com/a/42027/98739
\newcommand{\dfgExtractYear}[1]{\StrBefore[1]{#1}{-}}%
\newcommand{\dfgExtractMonth}[1]{\StrBetween[1,2]{#1}{-}{-}}%
\newcommand*{\dfgExtractDay}[1]{\StrBehind[2]{#1}{-}}%
% database
\DTLnewdb{name}
\DTLnewrow{name}
\DTLnewdbentry{name}{dateBirth}{1980-12-04}
\begin{document}
date: \get{name}{dateBirth}\ % works
Year: \dfgExtractYear{YYYY-MM-DD}\% works
Day: \dfgExtractDay{YYYY-MM-DD}\% works
Month: \dfgExtractMonth{YYYY-MM-DD}\% works
Only Year: \dfgExtractMonth{\get{name}{dateBirth}}% does not work
\end{document}

This is the result:

How can I combine the extraction code of the date-part with the entry of the database?

thank you, but i am not able to transfer the solution proposed their onto my code. any help appreciated — lukascbossert, Feb 05 '22 at 18:06

score 1 · Accepted Answer · answered Jul 24 '22 at 16:44

The explanation can be found in e.g. https://tex.stackexchange.com/a/632508/250119, or my answer in https://tex.stackexchange.com/a/646000/250119 (case 2.1.1), namely your defined \get is not fully expandable.

To fix this particular case, you must move \myload outside:

\documentclass{article}
\usepackage{xstring}
\usepackage{datatool}
\newcommand{\myload}[3][1]{%
  \DTLgetvalue
  {\thevalue}
  {#2}
  {#1}
  {\dtlcolumnindex
    {#2}
    {#3}}%
}
%\get{<DATABASE>}{<FIELD>}
\newcommand{\get}[3][1]{%
  \myload[#1]{#2}{#3}
   \thevalue%
  }
% https://tex.stackexchange.com/a/42027/98739
\newcommand{\dfgExtractYear}[1]{\StrBefore[1]{#1}{-}}%
\newcommand{\dfgExtractMonth}[1]{\StrBetween[1,2]{#1}{-}{-}}%
\newcommand*{\dfgExtractDay}[1]{\StrBehind[2]{#1}{-}}%
% database
\DTLnewdb{name}
\DTLnewrow{name}
\DTLnewdbentry{name}{dateBirth}{1980-12-04}
\begin{document}
date: \get{name}{dateBirth}\ % works
Year: \dfgExtractYear{YYYY-MM-DD}\% works
Day: \dfgExtractDay{YYYY-MM-DD}\% works
Month: \dfgExtractMonth{YYYY-MM-DD}\% works
Only Year: \myload{name}{dateBirth}\dfgExtractMonth{\thevalue}
\end{document}

(only the second-last line is changed). It's rather inconvenient.

Alternatively, for a convenient option, use the functional package to define both \get and \dfgExtractMonth, that way you'll be able to use \get inside an argument of \dfgExtractMonth, but currently it doesn't support optional argument (see Use \input with siunitx's \num and there are some workarounds)

Just to make this one answered, as I use this one as an example linked from my answer there. — user202729, Jul 24 '22 at 16:44

How to extract year from date in iso 8601 format?

1 Answers1

Linked