如何在matplotlib中绘制多个X或Y轴？

Question

我目前正在使用matplotlib绘制一个与x轴上的2或3个其他测量值（有时是分类的）相对应的测量值。目前，我正在将x轴上的数据分组成元组，并在绘制之前对它们进行排序。。。结果类似于下面的左图。我想做的是用多个x轴绘制数据，如右图所示。“治疗”x轴标签的分组将是锦上添花。

Answer 1

首先，很酷的问题！matplotlib>；=1.0.0绝对有可能。（新的spines功能允许它）

它需要一点巫毒，尽管。。。我的例子远非完美，但希望它有一定的意义：

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

def main():
    #-- Generate some data ----------------------------------------------------
    nx = 10
    x = np.linspace(0, 2*np.pi, 10)
    y = 2 * np.sin(x)

    groups = [('GroupA', (x[0], x[nx//3])),
              ('GroupB', (x[-2*nx//3], x[2*nx//3])),
              ('GroupC', (x[-nx//3], x[-1]))]

    #-- Plot the results ------------------------------------------------------
    fig = plt.figure()
    ax = fig.add_subplot(111)

    # Give ourselves a bit more room at the bottom
    plt.subplots_adjust(bottom=0.2)

    ax.plot(x,y, 'k^')

    # Drop the bottom spine by 40 pts
    ax.spines['bottom'].set_position(('outward', 40))

    # Make a second bottom spine in the position of the original bottom spine
    make_second_bottom_spine(label='Treatment')

    # Annotate the groups
    for name, xspan in groups:
        annotate_group(name, xspan)

    plt.xlabel('Dose')
    plt.ylabel('Response')
    plt.title('Experimental Data')

    plt.show()


def annotate_group(name, xspan, ax=None):
    """Annotates a span of the x-axis"""
    def annotate(ax, name, left, right, y, pad):
        arrow = ax.annotate(name,
                xy=(left, y), xycoords='data',
                xytext=(right, y-pad), textcoords='data',
                annotation_clip=False, verticalalignment='top',
                horizontalalignment='center', linespacing=2.0,
                arrowprops=dict(arrowstyle='-', shrinkA=0, shrinkB=0,
                        connectionstyle='angle,angleB=90,angleA=0,rad=5')
                )
        return arrow
    if ax is None:
        ax = plt.gca()
    ymin = ax.get_ylim()[0]
    ypad = 0.01 * np.ptp(ax.get_ylim())
    xcenter = np.mean(xspan)
    left_arrow = annotate(ax, name, xspan[0], xcenter, ymin, ypad)
    right_arrow = annotate(ax, name, xspan[1], xcenter, ymin, ypad)
    return left_arrow, right_arrow

def make_second_bottom_spine(ax=None, label=None, offset=0, labeloffset=20):
    """Makes a second bottom spine"""
    if ax is None:
        ax = plt.gca()
    second_bottom = mpl.spines.Spine(ax, 'bottom', ax.spines['bottom']._path)
    second_bottom.set_position(('outward', offset))
    ax.spines['second_bottom'] = second_bottom

    if label is not None:
        # Make a new xlabel
        ax.annotate(label, 
                xy=(0.5, 0), xycoords='axes fraction', 
                xytext=(0, -labeloffset), textcoords='offset points', 
                verticalalignment='top', horizontalalignment='center')

if __name__ == '__main__':
    main()