How can I place numbers into marks of a plot?

Question

I have the following plot

with this latex-source:

\documentclass{minimal}
\usepackage{tikz}
\usetikzlibrary{plotmarks}

%%%<
\usepackage{verbatim}
\usepackage[active,tightpage]{preview}
\PreviewEnvironment{tikzpicture}
\setlength\PreviewBorder{5pt}%
%%%>

% The data files, written on the first run.
\begin{filecontents}{function.data}
# n     m
1 1
1 2
2 1
1 3
2 2
3 1
1 4
2 3
3 2
4 1
1 5
2 4
3 3
4 2
5 1
\end{filecontents}

\begin{document}
\begin{tikzpicture}[y=.5cm, x=.5cm,font=\sffamily]
    %axis
    \draw (0,0) -- coordinate (x axis mid) (5,0);
        \draw (0,0) -- coordinate (y axis mid) (0,5);
        %ticks
        \foreach \x in {0,...,5}
            \draw (\x,1pt) -- (\x,-3pt)
            node[anchor=north] {\x};
        \foreach \y in {0,...,5}
            \draw (1pt,\y) -- (-3pt,\y) 
                node[anchor=east] {\y}; 
    %labels      
    \node[below=0.8cm] at (x axis mid) {n};
    \node[rotate=90, above=0.8cm] at (y axis mid) {m};

    %plots
    \draw plot[mark=square*]
        file {function.data};  

    %legend
    \begin{scope}[shift={(4,4)}] 
    \draw (0,0) -- 
        plot[mark=square*, mark options={fill=black}] (0.25,0) -- (0.5,0)
        node[right]{f(m, n)};
    \end{scope}
\end{tikzpicture}
\end{document}

Now I would like to place numbers into the marks or replace the marks by numbers. How is this possible?

Answer 1

I would use PGFplots for this, instead of building the plots by hand. In PGFplots, you can use the nodes near coords key for generating labels at each data point.

Here's your plot reproduced in PGFplots, with the labels.

\documentclass{article}
\usepackage{pgfplots}
\usepackage{sansmath} % for sans serif math

%%%<
% The data files, written on the first run.
\begin{filecontents}{function.data}
# n     m
1 1
1 2
2 1
1 3
2 2
3 1
1 4
2 3
3 2
4 1
1 5
2 4
3 3
4 2
5 1
\end{filecontents}

\begin{document}

\begin{tikzpicture}
\begin{axis}[
    compat=newest, % for better label placement
    font=\sansmath\sffamily, % math and normal text in sans serif
    xlabel=n, ylabel=m, % the label texts
    xmin=0, ymin=0, % axis origin
    enlarge y limits=false, % don't enlarge the y axis beyond the data range
    enlarge x limits={upper,abs=0.02}, % enlarge x axis slightly to make sure the last tick mark is drawn completely
    axis lines*=left, % only draw the left axis lines, not a box
    unit vector ratio*={1 1 1}, % equal axis scaling. "*" to make sure the axes can only be reduced in size, not enlarged
    width=6cm, % set the overall width of the plot
    try min ticks=5, % adjusts how many ticks are printed
    tick align=center, % tick marks centered on the axes
    legend style={
        draw=none, % no frame around axes
        at={(1,1)}, % place at upper right of plot
        anchor=north % use upper middle edge of legend for alignment
    },
]
\addplot [
    mark=square*, mark size=0.5em, % square, filled ("*"), radius of 0.5em
    nodes near coords={
        \pgfmathparse{int(\coordindex+1)}
        \pgfmathresult
    }, % print labels on each data point, using `\coordindex` (the data point counter) increased by 1
    every node near coord/.style={
        font=\scriptsize\sffamily\bfseries, % smaller text size, bold for the data point labels
        text=white,
        anchor=center % center the labels on the plot marks
    }
    ] table {function.data};
\addlegendentry{f(m,n)}
\end{axis}
\end{tikzpicture}
\end{document}