How to plot data from a CSV file using tikz and csvsimple?

If you need to plot data from files, I think you'll be much happier if you use PGFPlots instead of the native plot functionality of TikZ. Here's a very simple example of plotting your example data to get you started.

PGFPlots is very customizable, you can tweak virtually every aspect of your plots, and it's much more user-friendly than if you tried to knit everything yourself.

\documentclass{article}
\usepackage{pgfplots}
\usepackage{filecontents}
\begin{filecontents*}{data.csv}
a,b,c,d
1,4,5,1
2,3,1,5
3,5,6,1
4,1,4,9
5,3,4,7
\end{filecontents*}


\begin{document}
\begin{tikzpicture}
\begin{axis}
\addplot table [x=a, y=c, col sep=comma] {data.csv};
\end{axis}
\end{tikzpicture}
\end{document}

It seems that it's impossible to call csvreader inside \draw plot coordinates { }. To avoid the plot command and still being able to plot lines between points, I need to use xdef to remember the previous point.

\begin{filecontents*}{data.csv}
a,b,c,d
1,4,5,1
2,3,1,5
3,5,6,1
4,1,4,9
5,3,4,7
\end{filecontents*}

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{csvsimple}
\usepackage{tikz}

\begin{document}
\begin{tikzpicture}
    \csvreader[ head to column names,%
                late after head=\xdef\aold{\a}\xdef\bold{\b},%
                after line=\xdef\aold{\a}\xdef\bold{\b}]%
                {data.csv}{}{%
    \draw (\aold, \bold) -- (\a,\b) node {$\times$};
    }
\end{tikzpicture}
\end{document}

I get the output below. Now I can get back to work and print a whole bunch of data in my report ;-) I love it !

Another example with csvsimple, tikz and pgf-pie.

\begin{filecontents*}{newData.csv}
20,30,50
\end{filecontents*}

\documentclass[10pt,a4paper]{article}
\usepackage[utf8]{inputenc}

\usepackage{csvsimple}
\usepackage{tikz}
\usepackage{pgf-pie}

\begin{document}

\begin{tikzpicture}
\csvreader[no head]%
{newData.csv}
{1=\colVali,2=\colValii,3=\colValiii}
{%
  \pie[polar, explode=0.1]
  {\colVali/A, \colValii/B, \colValiii/C}
}
\end{tikzpicture}

\end{document}

Which produces the following pie chart: