给 ycomb 贴上标签

Question

我从两个文件中读取数据并绘制图表ycomb。我想计算值之间的差值并将其放在较大值的上方，如图所示。我该怎么做？

\documentclass{standalone}
\usepackage{tikz}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
\pgfplotsset{compat=newest}

\begin{document}

\begin{tikzpicture}
    \begin{axis} [
        enlarge y limits=0.5,
        ]
        \addplot+[ycomb,scatter] table[x=x,y=y]{
            y      x
            3      3
        };
        \addplot+[ycomb,scatter] table[x=x,y=y]{
            y      x
            5      3
        };
    \end{axis}
\end{tikzpicture}

\end{document}

Answer 1

也许有点绕弯子，可能还有更简单的方法，但这里有一个建议。代码中有一些注释表明会发生什么，如果有什么不清楚的地方，我可以添加更多细节。

开始时的内容filecontents只是为了使示例独立，当您已经有文件时，您不需要它。

\begin{filecontents*}{data1.dat}
            y      x
            3      3
            6      4
\end{filecontents*}
\begin{filecontents*}{data2.dat}
            y      x
            5      3
            2      4
\end{filecontents*}

\documentclass{standalone}
\usepackage{pgfplotstable} % loads pgfplots which loads tikz
\pgfplotsset{compat=newest}

% read data files to tables
\pgfplotstableread{data1.dat}{\dataA}
\pgfplotstableread{data2.dat}{\dataB}

% make two new columns to \dataB
% first column has absolute value of the difference between the y-values in the two files
\pgfplotstablecreatecol[
  create col/assign/.code={
   \pgfplotstablegetelem{\pgfplotstablerow}{y}\of\dataA
   \pgfmathparse{abs(\thisrow{y}-\pgfplotsretval)}
   \edef\entry{\pgfmathresult}
   \pgfkeyslet{/pgfplots/table/create col/next content}\entry
}
]{diff}{\dataB}
% the second column has the maximum of the two y-values
\pgfplotstablecreatecol[
  create col/assign/.code={
   \pgfplotstablegetelem{\pgfplotstablerow}{y}\of\dataA
   \pgfmathparse{max(\thisrow{y},\pgfplotsretval)}
   \edef\entry{\pgfmathresult}
   \pgfkeyslet{/pgfplots/table/create col/next content}\entry
}
]{max}{\dataB}

\begin{document}

\begin{tikzpicture}
    \begin{axis} [
        ymin=0
        ]
        \addplot+[ycomb] table[x=x,y=y]{\dataA};
        \addplot+[ycomb] table[x=x,y=y]{\dataB};

        % use third \addplot to add labels
        \addplot [
           only marks,mark=none, % don't actually plot anything visible
           nodes near coords, % add the labels to points
           nodes near coords align=above, % place labels above points
           point meta=explicit % so it reads from the meta column, instead of using the y-value
         ] table[x=x,y=max,meta=diff] {\dataB};
    \end{axis}
\end{tikzpicture}

\end{document}

Answer 2

当你将数据表合并为一个表时，很容易nodes near coords使用第三个表添加数据\addplot（如Torbjørn T.在他的回答中做了)。

（不添加第三个“虚拟”\addplot命令也可以实现相同的结果，但会更加复杂。）

有关详细信息，请查看代码中的注释。

% used PGFPlots v1.16
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\usepackage{pgfplotstable}
    % combine the data in one table
    \pgfplotstableread{
        x y1 y2
        3 3  5
    }{\data}
\begin{document}
\begin{tikzpicture}
    \begin{axis} [
        enlarge y limits=0.5,
        ycomb,
    ]
        % plot the
        \addplot table [x=x,y=y1] {\data};
        \addplot table [x=x,y=y2] {\data};

        % add the nodes near coords
        \addplot [
            % the plot itself should not be visible
            draw=none,
            % but we want to have the `nodes near coords' ...
            nodes near coords,
            % ... for which the values are explicitly given/calculated
            point meta=explicit,
            % only needed in case you want to add another `\addplot to not
            % change the cycle list index etc.
            forget plot,
        ] table [
            x=x,
            % add the `nodes near coords' at the larger of the two values ...
            y expr={max(\thisrow{y1},\thisrow{y2})},
            % ... and show the difference of the two values
            meta expr={abs(\thisrow{y1}-\thisrow{y2})},
        ] {\data};
    \end{axis}
\end{tikzpicture}
\end{document}