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pgfmathparse，foreach 在轴内不起作用

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pgfmathparse，foreach 在轴内不起作用

我尝试在里面使用foreach循环和。但它给了我一个错误。 pgfmathparseaxis

\documentclass[10pt,border=0pt]{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{siunitx}

% Default options for plots
\pgfplotsset{%
    compat=1.12,
    compat/show suggested version=false,
    %tick label style={font=\footnotesize},
    %label style={font=\footnotesize},
    legend style={%
        %draw=none,
        font=\footnotesize,
        at={(0.5,1.0)}, % position of legend
        yshift=3pt,
        anchor=south,
        legend columns=2
        legend cell align=left,
        inner xsep=2pt,
        /tikz/column 2/.style={%
            column sep=4pt, % http://tex.stackexchange.com/questions/80215/two-columns-in-legend-in-pgfplots
        },
        /tikz/column 1/.style={%
            column sep=2pt,
        },
        /tikz/column 3/.style={%
            column sep=2pt,
        },
        nodes={inner xsep=0pt,inner ysep=0pt,text depth=0.15em},
        %nodes={inner xsep=2pt,inner ysep=0pt,text depth=0.15em}, % this added a space after the last text 
    },
}


\begin{document}
\begin{tikzpicture}
\begin{axis}[%
    width=20cm,
    ybar stacked,
    bar width=1cm,
    ylabel={YLABEL},
    symbolic x coords={a,b,c,d,e,f},
    ticks=none,
    %xtick={a,b,c,d,e,f}, % adds legend at ticks
    %enlarge x limits=0.5,
    %enlarge x limits,
    enlarge y limits=0.2,
    nodes near coords,
    font=\footnotesize,
    grid=major,
    after end axis/.code={% http://tex.stackexchange.com/questions/55261/labeling-the-axes-of-my-plot
        \node[below] at (xticklabel cs:0.25) {XXX};
        \node[below] at (xticklabel cs:0.75) {YYY};
    }
]

    \addplot coordinates {(a,5.42) (b,13.4) (c,10.69) (d,10.81) (e,30.31) (f,22.53)};
    \addplot coordinates {(a,0.72) (b,17.87) (c,5) (d,1.40) (e,12.39) (f,5.17)};
    \legend {Downlink,Uplink};

    \foreach \x/\y in {1/a,2/b,3/c,4/a,5/b,6/c)} {%
        \pgfmathsetmacro{\coor}{\x*(0.5/6)}
        \node[draw,anchor=south west] at (rel axis cs:\coor,0.8) {\y};
    };
\end{axis}

\end{tikzpicture}
\end{document}

答案1

pgfplots手册第 8.1 节中描述了此情况的原因实用程序命令。我引用相关内容：

请记住，在axis环境中，所有循环构造（包括自定义循环 \foreach和\pgfplotsforeachungrouped）都需要小心处理：循环参数只能在立即求值的地方使用；但pgfplots会推迟许多宏的求值。例如，要循环某些东西并生成形式为的轴描述\node at (axis cs:\i,0.5)....，循环宏\i将在中求值\end{axis}——但此时，循环结束并且其值丢失。处理此类应用程序的正确方法是显式扩展循环变量。例如：

\pgfplotsforeachungrouped \i/\j in {
1 / a,
2 / b,
3 / c
}{
\edef\temp{\noexpand\node at (axis cs: \i,0.5) {\j};}
% \show\temp % lets TeX show you what \temp contains
\temp
}

该示例生成三个循环迭代：\i=1，\j=a；然后\i=2，j=b；然后\i=3，\j=c。在循环体内部，它使用“扩展定义” \edef 扩展它们并将结果分配给宏。结果不再包含 或\i（\j因为它们已被扩展）。然后，它调用结果宏。有关 TEX 命令\edef和扩展控制的详细信息可以在 随附的文档 TeX-programming-notes.pdf 中找到pgfplots。

因此使用上述结构循环就可以工作：

\documentclass[10pt,border=0pt]{standalone}

\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{siunitx}

% Default options for plots
\pgfplotsset{%
    compat=1.12,
    compat/show suggested version=false,
    %tick label style={font=\footnotesize},
    %label style={font=\footnotesize},
    legend style={%
        %draw=none,
        font=\footnotesize,
        at={(0.5,1.0)}, % position of legend
        yshift=3pt,
        anchor=south,
        legend columns=2
        legend cell align=left,
        inner xsep=2pt,
        /tikz/column 2/.style={%
            column sep=4pt, % http://tex.stackexchange.com/questions/80215/two-columns-in-legend-in-pgfplots
        },
        /tikz/column 1/.style={%
            column sep=2pt,
        },
        /tikz/column 3/.style={%
            column sep=2pt,
        },
        nodes={inner xsep=0pt,inner ysep=0pt,text depth=0.15em},
        %nodes={inner xsep=2pt,inner ysep=0pt,text depth=0.15em}, % this added a space after the last text 
    },
}


\begin{document}
\begin{tikzpicture}
\begin{axis}[%
    width=20cm,
    ybar stacked,
    bar width=1cm,
    ylabel={YLABEL},
    symbolic x coords={a,b,c,d,e,f},
    ticks=none,
    %xtick={a,b,c,d,e,f}, % adds legend at ticks
    %enlarge x limits=0.5,
    %enlarge x limits,
    enlarge y limits=0.2,
    nodes near coords,
    font=\footnotesize,
    grid=major,
    after end axis/.code={% http://tex.stackexchange.com/questions/55261/labeling-the-axes-of-my-plot
        \node[below] at (xticklabel cs:0.25) {XXX};
        \node[below] at (xticklabel cs:0.75) {YYY};
    }
]

    \addplot coordinates {(a,5.42) (b,13.4) (c,10.69) (d,10.81) (e,30.31) (f,22.53)};
    \addplot coordinates {(a,0.72) (b,17.87) (c,5) (d,1.40) (e,12.39) (f,5.17)};
    \legend {Downlink,Uplink};

    \foreach \x/\y in {1/a,2/b,3/c,4/a,5/b,6/c} {%
        \pgfmathsetmacro{\coor}{\x*(0.5/6)}
%        \node[draw,anchor=south west] at (rel axis cs:\coor,0.8) {\y};
        \edef\temp{\noexpand\node at (rel axis cs: \coor,0.8) {\y};}
        \temp
    };
\end{axis}

\end{tikzpicture}
\end{document}

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