Retrieve specific values from csv using Datatool and divide them by each other

Question

So I am loading a csv file that looks something like this:

est;dens;mwp
ols11;0.1;.
ols12;0.09;0.001

I want to use the following code to divide two numbers. I use the .csv in a table, but I also refer to them in the text, and would like this to be automated. But I get the following error from the code: Missing number, treated as zero. for the line \basiceval{\x/\y}. I am not very experienced with evaluating numbers in LaTex, so any help would be appreciated!

\documentclass{article}

\usepackage{datatool}
\DTLsetseparator{;}
\DTLloaddb{mun_reg}{63_mun_result.csv}
\def\basiceval#1{\the\numexpr#1\relax}

\begin{document}
\def\x{\DTLfetch{mun_reg}{est}{ols11}{dens}}
\def\y{\DTLfetch{mun_reg}{est}{ols12}{dens}}
\basiceval{\x/\y}

\end{document}

Answer 1

There are two issues with the approach in the question: first \numexpr performs integer division, so you can't use it for 0.1/0.09, and second the \DTLfetch statement is not expanded in the \def, so you essentially try to divide a (very complex) macro by another macro, instead of dividing two numbers as you expect.

To perform calculations on decimal numbers datatool has some built-in mathematical functions, among which \DTLdiv (for division). The input of these functions is supposed to be a macro holding a value, and the result is also stored in a macro. For storing database values in a macro you can use \DTLgetvalueforkey instead of \DTLfetch. Note that for \DTLgetvalueforkey the order of the column and row specification is different (first the column for which you want to find the value, then the reference column and row).

For more information on the mathematical functions you can read section 3 of the manual, specifically page 24 and further.

MWE:

\documentclass{article}
\usepackage{datatool}
\DTLsetseparator{;}
\DTLloaddb{mun_reg}{63_mun_result.csv}

\begin{document}
\DTLgetvalueforkey{\myx}{dens}{mun_reg}{est}{ols11}
\DTLgetvalueforkey{\myy}{dens}{mun_reg}{est}{ols12}
\DTLdiv{\mydiv}{\myx}{\myy}
Result: \mydiv
\end{document}