如何在 pgfplots 上自定义图例？

Question

我正在尝试设计一个类似图片的图例。它有两列，每列都有标题文本。此外，我如何控制第一列中的哪个项目以及第二列中的哪个项目？

    \documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.6}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[
        legend columns=2, 
        legend style={
                    % the /tikz/ prefix is necessary here...
                    % otherwise, it might end-up with `/pgfplots/column 2`
                    % which is not what we want. compare pgfmanual.pdf
            /tikz/column 2/.style={
                column sep=5pt,
            },
        },
    ]
        \addplot {x};
        \addlegendentry{ }
        \addplot {x+4};
        \addlegendentry{$x$+4}‎
        ‎
          \addplot {2*x};
        \addlegendentry{ }
        \addplot {2*x+4};
        \addlegendentry{$2x$+4}‎
        ‎
        ‎
         \addplot {4*x};
        \addlegendentry{ }
        \addplot {4*x+4};
        \addlegendentry{$4x$+4}
    \end{axis}
\end{tikzpicture}

\end{document}

Answer 1

在下面的解决方案中，我使用了作者本人在在 pgfplot 中的图例中添加自定义条目以及在 pgfplots 中正确对齐基线上的垂直文本这使：

我已将图例单元格与左侧对齐，并将图例放在东南方，但您当然可以根据需要进行更改：)

% arara: pdflatex
% !arara: indent: {overwrite: yes}
\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.6}

% https://tex.stackexchange.com/questions/84127/correctly-align-vertical-text-on-a-baseline-in-pgfplots
\def\mystrut{\vphantom{hg}}

% https://tex.stackexchange.com/questions/204395/add-custom-entry-into-legend-in-pgfplot
\pgfplotsset{
    legend image with text/.style={
        legend image code/.code={%
            \node[anchor=center] at (0.3cm,0cm) {#1};
        }
    },
}

\begin{document}

\begin{tikzpicture}
    \begin{axis}[
            legend columns=2,
            legend style={
                font=\mystrut,
                legend cell align=left,
            },
            legend pos=south east,
        ]
        % column 1 heading
        \addlegendimage{legend image with text=$ax$}
        \addlegendentry{}
        % column 2 heading
        \addlegendimage{legend image with text=$ax+4$}
        \addlegendentry{}
        % the plots of the functions follow
        \addplot {x};
        \addlegendentry{}
        \addplot {x+4};
        \addlegendentry{$x+4$}
        \addplot {2*x};
        \addlegendentry{}
        \addplot {2*x+4};
        \addlegendentry{$2x+4$}
        \addplot {4*x};
        \addlegendentry{}
        \addplot {4*x+4};
        \addlegendentry{$4x+4$}
    \end{axis}
\end{tikzpicture}

\end{document}

Answer 2

可能有更简单的方法可以做到这一点，但这肯定是最适合的。（别忘了运行两次。）

\documentclass{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.6}

\begin{document}

\begin{tikzpicture}
  \begin{axis}[name=boundary]
    \addplot {x};\label{pgfplots:c1r1}
    \addplot {x+4};\label{pgfplots:c2r1}

    \addplot {2*x};\label{pgfplots:c1r2}
    \addplot {2*x+4};\label{pgfplots:c2r2}

    \addplot {4*x};\label{pgfplots:c1r3}
    \addplot {4*x+4};\label{pgfplots:c2r3}
  \end{axis}
  \node[draw,fill=white,inner sep=0pt,above left=0.5em] at (boundary.south east) {\small
    \begin{tabular}{ccl}
    $ax$ & $ax+4$ \\
    \ref{pgfplots:c1r1} & \ref{pgfplots:c2r1} & $a=1$\\
    \ref{pgfplots:c1r2} & \ref{pgfplots:c2r2} & $a=2$\\
    \ref{pgfplots:c1r3} & \ref{pgfplots:c2r3} & $a=4$
    \end{tabular}};
\end{tikzpicture}

\end{document}

Answer 3

该解决方案与以下解决方案非常相似约翰·科米洛但使用\matrix相应库中的节点来生成自定义图例。

（本回答改编自这重复问题答案。

% used PGFPlots v1.14
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
    % load `matrix' library so we can use the `matrix of nodes' feature
    \usetikzlibrary{
        matrix,
    }
\begin{document}
    \begin{tikzpicture}
        \begin{axis}[
            % just because it looks a bit better than the default
            cycle list name=exotic,
        ]
            \addplot {x};       \label{plot:line1}
            \addplot {x+4};     \label{plot:line2}

            \addplot {2*x};     \label{plot:line3}
            \addplot {2*x+4};   \label{plot:line4}

            \addplot {4*x};     \label{plot:line5}
            \addplot {4*x+4};   \label{plot:line6}

            % create a (dummy) coordinate where we want to place the legend
            %
            % (The matrix cannot be placed inside the `axis' environment
            %  directly, because then a catcode error is raised.
            %  I guess that this is caused by the `matrix of nodes' feature)
            \coordinate (legend) at (axis description cs:0.97,0.03);
        \end{axis}

        % create the legend matrix which is placed at the created (dummy) coordinate
        % and recall the plot specification using the `\ref' command
        %
        % adapt the style of that node to your needs
        % (e.g. if you like different spacings between the rows or columns
        %  or a fill color)
        \matrix [
            draw,
            matrix of nodes,
            anchor=south east,
        ] at (legend) {
            $ax$             & $ax+4$           &       \\
            \ref{plot:line1} & \ref{plot:line2} & $a=1$ \\
            \ref{plot:line3} & \ref{plot:line4} & $a=2$ \\
            \ref{plot:line5} & \ref{plot:line6} & $a=4$ \\
        };

    \end{tikzpicture}
\end{document}