如何根据 y 轴值更改 pgfplots 中图形点的颜色

Question

我正在尝试编写一些 tikz 代码，以便图表可以在文档中重复多次，并保持一致的格式。

一切进展顺利，直到我决定根据在“\myGraph”中输入的值来改变点的颜色。

所有大于 5 的值都应显示为红色，所有小于 5 的值都应显示为绿色。

我能想到的最好的办法如下，我认为我编写的代码有效地使中间点（最小/最大数据值）以上的所有值变为红色，中间点以下的所有值变为绿色。因此，在某些情况下这样做没问题，但在其他情况下则不行。

我需要换线

\ifdim\pgfplotspointmetatransformed pt<500pt

类似于

\ifdim\pgfplotspointmeta pt<5

但这不起作用。有人能帮忙吗？

非常感谢！

\documentclass{article}
\usepackage{tikz,pgfplots}
\newcommand{\myGraph}[3]
{   
\begin{tikzpicture}[scale=0.5]
\begin{axis}[
scatter/@pre marker code/.code={%
    \ifdim\pgfplotspointmetatransformed pt<500pt
        \def\markopts{fill=green}%
    \else
        \def\markopts{fill=red}
     \fi
    \expandafter\scope\expandafter[\markopts]
},%
 scatter/@post marker code/.code={%
     \endscope
 },enlargelimits=0.1,ymin=0,ymax=10,/pgf/number format/1000 sep={}]
\addplot[scatter, line width=3pt, black,dashed, mark=*, mark options=     {scale=4,solid}] coordinates {%
(2017, #1)
(2019, #2) 
(2021, #3)
};
\end{axis}
\end{tikzpicture}
}

\begin{document}
First points should be green (2017,2019), last point should be red (2021).
\myGraph{1}{2}{7}

First point and last should be red (2017,2021), middle point should be green    (2019).

\myGraph{9}{4}{9}

But ... 

\myGraph{7}{7}{8}

all points should be red. 

\end{document}

Answer 1

您只需使用提供给键的数学函数并定义由所需颜色组成的point meta自定义即可获得所需的结果。colormap

% used PGFPlots v1.14
\documentclass[border=5pt]{standalone}
\usepackage{pgfplots}
\newcommand{\myGraph}[3]{
    \begin{tikzpicture}[scale=0.5]
        \begin{axis}[
            enlargelimits=0.1,
            ymin=0,
            ymax=10,
            /pgf/number format/1000 sep={},
            % create custom colorbar for the two colors you need
            colormap={my colormap}{
                color=(green)
                color=(red)
            },
        ]
            \addplot [
                scatter,
                line width=3pt,
                black,
                dashed,
                mark=*,
                mark options={scale=4,solid},
                % ---
                % apply here the function you need for the meta data
                point meta={ifthenelse(y>5,1,0)},
                % ... and set the limits of the `point meta' data (by hand)
                % (the automatic approach doesn't work if only 1 value is
                %  present which is the case for the third example)
                point meta min=0,
                point meta max=1,
            ] coordinates {
                (2017, #1)
                (2019, #2)
                (2021, #3)
            };
        \end{axis}
    \end{tikzpicture}
}
\begin{document}
    \myGraph{1}{2}{7}
    \myGraph{9}{4}{9}
    \myGraph{7}{7}{8}
\end{document}