[Tex/LaTex] How to use parameter numbers and \foreach

foreachloopsmacrostikz-pgf

Is there a way to use the TikZ \foreach command to do operations with parameters?

E.g. I would like to be able to write (just a silly example):

\newcommand{\foo}[9]{

    \foreach \x in{1,2,...,9}{
        \draw(0,#\x)--++(1,1);

    }
}

where #\x would mean the x th parameter of the command I'm defining with \newcommand.

This should come in handy since I'm writing macros that depend on global values that can be set arbitrarily. E.g. \def\N{9} would go in preamble and I'd write newcommand{\bar}[\N]{...}, but since I don't know beforehand how much parameters there will be, I can't define anything unless I write \foreach \x in{1,2,...,\N} and the above draw command.

What I actually like to do:

I'd like to have a command that plots some coordinates which are given.
So I'd like \foo{#1}{#2}{#3} to expand to something like;

\draw plot coordinates {(360/\N*1:#1) (360/\N*2:#2) (360/\N*3:#3) ... (360/\N*\N:#N};

but I don't know if this is possible.

Best Answer

I do not reall understand what exactly do you want to draw, but maybe this helps:

\documentclass{minimal}
\usepackage{tikz}

\makeatletter
\def\foo#1{\foo@i#1,,\@nil}%
\def\foo@i#1,#2,#3\@nil{%
  \draw(0,#1)--++(1,1);
  \ifx\relax#2\relax\else\foo@i#2,#3\@nil\fi}
\makeatother

\begin{document}
\begin{tikzpicture}
\foo{1,2,3,4,5,6,7,8,9}
\end{tikzpicture}
\begin{tikzpicture}
\foo{1,2,3,4,5,6}
\end{tikzpicture}

\end{document}

Related Solutions

[Tex/LaTex] TikZ: can I get an arbitrary list format for foreach

You can use / instead of -. You also need to wrap the coordinates in {} (see the comments on this answer by Martin if you wish to know why), then your example would become:

\documentclass{article}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}
\foreach \pointA/\pointB in {{(1,0)}/{(2,2)},{(3,4)}/{(2,1)}}{
  \draw \pointA -- \pointB;
}
\end{tikzpicture}
\end{document}

This can also be extended to more than 2 elements, just add another / \pointC. All of this is treated on page 506 of the Tikz manual.

EDIT Ok, after your edit (better to specify that, otherwise Peter and I look silly ;)), my answer isn't all that great anymore. Basically you can't do what you want due to the same reasons as in the comment I referenced above. You can work around it though. Note: this is just something hacked together quickly, it probably doesn't handle everything great, but it handles your MWE and can probably be extended.

\documentclass{article}
\usepackage{tikz}
\usetikzlibrary{calc}
\newcounter{n}
\makeatletter
\def\wrap(#1)#2{%
    \stepcounter{n}%
    \coordinate (\number\value{n}) at (#1);%
    \if#2(%
        \wraprest#2%
    \else\fi%
}
\def\wraprest(#1)#2{%
    \stepcounter{n}%
    \coordinate (\number\value{n}) at (#1);%
    \if#2(% 
        \wrap#2%
    \else\fi%
}
\begin{document}
\begin{tikzpicture}
\wrap(1,0)(2,0)(3,0)(4,0)(5,0)(6,0)(7,0)(8,0)x%
\foreach \pointA in {1,3,...,\number\value{n}}{
    \pgfmathsetmacro{\pointB}{\pointA+1}
  \draw (\pointA) -- (\pointB);
}
\end{tikzpicture}
\makeatother
\end{document}

This uses Peter's method of defining coordinates and using those in the list. First a coordinate is created for each (x,y) and these are numbered, such that lines go from n to n+1 where n is odd. If you want delimiters between pairs those can be added with a slight modification. (The x at the end of the wrap can be anything, just not ().

[Tex/LaTex] Tikz: \foreach and axis environment incompatibility

If you're using an axis environment, which is provided by the PGFPlots package, you should use \addplot instead of \plot.

To use a different colour for each plot, one option might be using the mesh plot type together with point meta=explicit and meta expr=\i. This allows the use of colormaps instead of being limited to colorA!<value>!colorB expressions:

\documentclass{article}
\usepackage{pgfplots}  % Loads all required packages automatically
\usepackage{filecontents}
\begin{filecontents*}{file1.txt}
0 0
1 1
2 2
3 1
4 0
\end{filecontents*}
\begin{filecontents*}{file2.txt}
0 1
1 3
2 5
3 3
4 1
\end{filecontents*}
\begin{filecontents*}{file3.txt}
0 2
1 5
2 7
3 5
4 2
\end{filecontents*}

\begin{document}

\begin{figure}
    \begin{tikzpicture} 
    \newcommand{\filename}{file}
    \begin{axis}[
            colormap/bluered
        ]
        \foreach \i in {1,2,3}
        {
            \addplot +[thick, no markers, mesh, point meta=explicit] table [meta expr=\i] {\filename \i.txt};
        }   
        \end{axis}
    \end{tikzpicture}
\end{figure}

\end{document}

Alternatively (and probably better), you can use the contour prepared plot style if you put all contours into a single file. That way, you can even get labels on the contours (the labels can be adjusted or switched off, of course):

\documentclass{article}
\usepackage{pgfplots}  % Loads all required packages automatically
\pgfkeys{/pgf/number format/relative round mode=fixed}
\usepackage{filecontents}
\begin{filecontents*}{contours.txt}
0 0 0
1 1 0
2 2 0
3 1 0
4 0 0

0 1 1
1 3 1
2 5 1
3 3 1
4 1 1

0 2 2
1 5 2
2 7 2
3 5 2
4 2 2
\end{filecontents*}

\begin{document}

\begin{figure}
    \begin{tikzpicture} 
    \newcommand{\filename}{file}
    \begin{axis}
    \addplot [contour prepared] table {contours.txt};
        \end{axis}
    \end{tikzpicture}
\end{figure}

\end{document}

Best Answer

Related Solutions

[Tex/LaTex] TikZ: can I get an arbitrary list format for foreach

[Tex/LaTex] Tikz: \foreach and axis environment incompatibility

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