How to put content from multiple databases in one table using datatool?

Question

Almost too easy:

I have two databases "First" and "Second", both get their data from tab-delineated files "First.txt" and "Second.txt"

Both contain two columns ('year' and 'number') and an equal amount of rows!

This code :

\begin{document}

\catcode`\^^I=12 %
\DTLsetseparator{   }%

\DTLloaddb{First}{First.txt}
\DTLloaddb{Second}{Second.txt}

\begin{table}[htbp]
\caption{First}
\centering
\DTLdisplaydb{First} 
\end{table}

\begin{table}[htbp]
\caption{Second}
\centering
\DTLdisplaydb{Second} 
\end{table}

\end{document}

creates two separate tables, but I am trying to make a table containing three columns: year, number (from First), number (from Second).

I know it sounds trivial (and probably is)... but I am stuck.

Anyone any idea?

Answer 1

Here's a way of appending the second column of the second database to the first database. (I've used comma-separated values rather than tab separated for simplicity, but you can changed that as required.) This assumes that both databases have their rows in the same order (on the first column).

\documentclass{article}

\usepackage{datatool}

% generate first test database
\begin{filecontents}{first.csv}
Year,Number
2001,10
2002,20
2003,30
2004,40
\end{filecontents}

% generate second test database
\begin{filecontents}{second.csv}
Year,Number
2001,101
2002,202
2003,303
2004,404
\end{filecontents}

\DTLloaddb{first}{first.csv}
\DTLloaddb{second}{second.csv}

\begin{document}

% append second column of second data base to first data base

\newcount\rowIdx

\dtlforcolumn{\secondNumber}{second}{Number}%
{%
  % iterate through each entry in the `Number' column of the second database
  \advance\rowIdx by 1\relax
  % get corresponding row of first database
  \dtlgetrow{first}{\rowIdx}%
  % append to current row (this new column is assigned the key `Number2')
  \dtlappendentrytocurrentrow{Number2}{\secondNumber}%
  % update first database
  \dtlrecombine
}

\DTLdisplaydb{first}

\end{document}

The result looks like:

Answer 2

This uses the readarray package to input the datafiles into "array" data structures (here named first and second). Then those array elements can be regurgitated in the table. The only quirk, for which I used a solution based on that provided by Herbert in How to programmatically make tabular rows using `\whiledo` ?, is that the \whiledo used to construct each row of the table has to be performed outside of the tabular environment. In particular, it is the presence of tab characters & inside the \whiledo inside the tabular that is somehow the problem (resolved by Herbert).

\documentclass{article}
\usepackage{readarray}
\newcounter{index}
  % Based on:
  % https://tex.stackexchange.com/questions/7590/
  % how-to-programmatically-make-tabular-rows-using-whiledo
  \makeatletter
  \newcounter{tabindex}
  \newtoks\@tabtoks
  \newcommand\addtabtoks[1]{%
    \@tabtoks\expandafter{\the\@tabtoks\stepcounter{tabindex}#1}}
  \newcommand*\resettabtoks{\@tabtoks{}}
  \newcommand*\synctabindex[1]{\setcounter{tabindex}{\value{#1}}}
  \newcommand*\printtabtoks{\the\@tabtoks}
  \makeatother
\begin{document}
\readdef{First.txt}{\tmpa}
\readArrayij{\tmpa}{first}{\ncols}
\readdef{Second.txt}{\tmpb}
\readArrayij{\tmpb}{second}{\ncols}
%
\resettabtoks
\setcounter{index}{0}
\synctabindex{index}
\whiledo{\value{index} < \nrows}{%
  \addtocounter{index}{1}%
  \addtabtoks{%
    \arrayij{first}{\thetabindex}{1} &
    \arrayij{first}{\thetabindex}{2} &
    \arrayij{second}{\thetabindex}{2} 
    \ifthenelse{\equal{\thetabindex}{\nrows}}{}{\\}%
  }
}
\begin{tabular}{|c|r|r|}
  \hline
  \printtabtoks
  \\\hline
\end{tabular}
\end{document}