Creating a heatmap using calculations and tabular environment

Question

I know there exists pgf, and many people uses this to create heatmaps. I however am not allowed to use this package. I therefore want to create a command that enables me to color the different cells.

I found this question, that showed the following def

\def\cca#1{\cellcolor{black!#10}\ifnum #1>5\color{white}\fi{#1}}

But it does only work from 0-9 as per his comments and my tests.

I wanted to create something more generic like this pseudo code:

\newcommand{\cTab}[2]
{
    \res = #1/#2 %maybe using FP (?)
    \eighty = 0.8*#2 %maybe using FP (?)

    \cellcolor{black!\res} 
    \ifnum #1>\eighty 
       \color{white}
    \fi{#1}
}

So basicly the issue is to calculate a number and then reuse it to define color and other?

I can calculate the number using FP, but not reuse it within cellcolor or ifnum.

MWE

\documentclass[letterpaper, 10 pt]{article}

% Color
\usepackage{xcolor,colortbl}%

\begin{document}
\begin{table}[!ht]
\centering
\caption{True data classification.}
\label{tab:CollectedErrors}
\begin{tabular}{|p{1.5cm}|p{0.5cm}|}
\hline
\textbf{Exposure}& \textbf{Attribute} \\ \hline

  4 & 2 \\ \hline
   11 &144 \\ \hline 
\end{tabular}
\end{table}
\end{document}

Basicly what I want is to create a heatmap, i.e. color cells based on the number within the cell in the table.

MWE using code from solution 1

\documentclass[letterpaper, 10 pt]{article}

% Color
\usepackage{xcolor,colortbl}%
\usepackage{xintexpr}

\newcommand{\cTab}[2]
{%
    \edef\res    {\xinttheiexpr [2] #1/#2\relax}% [2] = "two digits after ."
    \edef\eighty {\xinttheiexpr [2] 0.8*#2\relax}%
    \cellcolor{black!\res}%
    \xintifboolexpr {#1>\eighty}
        % yes branch 
           {\color{white}}
        % no branch (nothing to do)
           {}% 
    {#1}%
}%

\begin{document}
\begin{table}[!ht]
\centering
\caption{True data classification.}
\label{tab:CollectedErrors}
\begin{tabular}{|p{1.5cm}|p{0.5cm}|}
\hline
\textbf{Exposure}& \textbf{Attribute} \\ \hline

  \cTab{4}{4} & 2 \\ \hline %example, could also be \cTab{4}{144}, in theory all cells should be changed to cTab
   11 &144 \\ \hline 
\end{tabular}
\end{table}
\end{document}

Answer 1

You could try

\usepackage{xintexpr}

\newcommand{\cTab}[2]
{%
    \edef\res    {\xinttheiexpr [2] #1/#2\relax}% [2] = "two digits after ."
    \edef\eighty {\xinttheiexpr [2] 0.8*#2\relax}%
    \cellcolor{black!\res}%
    \xintifboolexpr {#1>\eighty}
    % yes branch 
       {\color{white}}
    % no branch (nothing to do)
       {}% 
    {#1}%
}%

But a mwe would help. Ok, mwe showed I needed \xdef\res but I am quite in the dark about what is aimed at. Update to explain I better understand now... (I was confused about xcolor color specification with a ! as I was led to believe it needed a number between 0 and 1, whereas a percentage between 0 and 100 is asked for).

Updated to avoid defining macros \res and \eighty (especially \res was annoying as it needed a global scope; but we can use expandability of \xinttheiexpr here).

\documentclass[letterpaper, 10 pt]{article}

% Color
\usepackage{xcolor,colortbl}

% Fine stuff
\usepackage{xintexpr, xinttools}

\newcommand{\cTab}[2]% #1 = cell, #2 = max
{%
    \cellcolor{black!\xinttheiexpr 100*#1/#2\relax}%
    \xintifboolexpr {#1>0.8*#2}%
    % "yes" branch 
       {\textcolor{blue}{#1}}% when #1 is big, print it blue
    % "no" branch
       {#1}% 
}%

\begin{document}
\begin{table}[!ht]
\centering
\caption{True data classification.}
\label{tab:CollectedErrors}
\smallskip
\begin{tabular}{|p{1.5cm}|c|}
\hline
\textbf{Exposure}& \textbf{Attribute} \\ \hline
\xintFor* #1 in {\xintSeq[3]{1}{100}}\do
{%
  \cTab{#1}{100} & \cTab{\the\numexpr100-#1\relax}{100}\\
}
\hline 
\end{tabular}
\end{table}
\end{document}

Notice also the use of \textcolor.