Record-like data structure?

Question

I would need something like this:

\setfield{record1}{field1}{alpha}
\setfield{record1}{field2}{beta}
\setfield{record2}{field1}{gamma}
\setfield{record2}{field2}{delta}
\assign{record3}{record2}
\getfield{record1}{field1} % should expand to alpha
\getfield{record1}{field2} % should expand to beta
\getfield{record2}{field1} % should expand to gamma
\getfield{record2}{field2} % should expand to delta
\getfield{record3}{field1} % should expand to gamma
\getfield{record3}{field2} % should expand to delta

Is there a package for this? I could live without the assign command.

Answer 1

Essentially \setfield is a \def where the control sequence name is constructed using the first two arguments. \getfield merely sets the requested control sequence (no error checking is performed; \csname ... \endcsname returns \relax if the record/field does not exist).

\documentclass{article}

\usepackage{etoolbox}

\newcommand{\setfield}[3]{%
  \expandafter\def\csname #1@#2\endcsname{#3}%
  \listcsgadd{#1}{#2}%
}
\newcommand{\getfield}[2]{%
  \ifcsname #1@alias\endcsname
    \expandafter\expandafter\expandafter\csname \csname #1@alias\endcsname @#2\endcsname
  \else
    \csname #1@#2\endcsname
  \fi}
\newcommand{\recordalias}[2]{\expandafter\def\csname #2@alias\endcsname{#1}}
\newcommand{\recordcopy}[2]{%
  \renewcommand*{\do}[1]{%
    \expandafter\edef\csname #2@##1\endcsname{\csname #1@##1\endcsname}}%
  \dolistcsloop{#1}%
}

\begin{document}

\setfield{record1}{field1}{alpha}
\setfield{record1}{field2}{$\beta$}
\setfield{record2}{field1}{gamma}
\setfield{record2}{field2}{$\delta$}

\recordalias{record2}{record3}
\recordcopy{record2}{record4}

\getfield{record1}{field1} % should expand to alpha
\getfield{record1}{field2} % should expand to $\beta$
\getfield{record2}{field1} % should expand to gamma
\getfield{record2}{field2} % should expand to $\delta$
\getfield{record3}{field1} % should expand to gamma
\getfield{record3}{field2} % should expand to $\delta$

\setfield{record2}{field1}{$\gamma$}

\getfield{record2}{field1} % should expand to $\gamma$
\getfield{record3}{field1} % should expand to $\gamma$
\getfield{record4}{field1} % should expand to gamma

\end{document}

Added are two types of assignments:

• alias via \recordalias{<first>}{<second>} - this makes the <second> record an alias for <first>;
• copy via \recordcopy{<first>}{<second>} - this sequentially copies all the fields from <first> into <second> using list processing provided by etoolbox.

Answer 2

\documentclass[10pt]{article}
\usepackage{readarray}
\begin{document}
\readarraysepchar{ }
\def\mydata{alpha beta gamma delta}
\readarray\mydata\myarray[-,2]% Read \mydata as 2 fields into 2-D \myarray
Cell (2,2) has \myarray[2,2]
whereas cell (1,2) has \myarray[1,2]
\end{document}

If the data is in a file, also no problem. Note that \readdef, while reading the file, sets \ncols to the number of fields detected in the first row and can be used, instead of an explicit 2, for the \readarray. I also demonstrate the use of a different separator (comma instead of space) and show how the * option of \readarray will remove leading and trailing spaces.

\documentclass[10pt]{article}
\usepackage{readarray,filecontents}
\begin{filecontents*}{mydatafile}
alpha, beta
gamma, delta force
\end{filecontents*}
\begin{document}
\readarraysepchar{,}
\readdef{mydatafile}{\mydata}
\readarray*\mydata\myarray[-,\ncols]% Read \mydata as 2 fields into 2-D \myarray
Cell (2,2) has \myarray[2,2]
whereas cell (1,2) has \myarray[1,2]
\end{document}

FINALLY, if changing cell data on the fly is a requirement, I implement here the macro \setfield\<array name>[<row>,<column>]{<data>}:

\documentclass[10pt]{article}
\usepackage{readarray}
\makeatletter
\gdef\setfield#1[#2,#3]#4{%
  \expandafter\gdef\csname\expandafter\@gobble\string#1[#2,#3]\endcsname{#4}}%
\makeatother
\begin{document}
\readarraysepchar{ }
\def\mydata{alpha beta gamma delta}
\readarray\mydata\myarray[-,2]% Read \mydata as 2 fields into 2-D \myarray
Cell (2,2) has \myarray[2,2]
whereas cell (1,2) has \myarray[1,2]

\setfield\myarray[1,2]{$\beta$}
Cell (1,2) now has \myarray[1,2].
\end{document}