matplotlib轴箭头提示

Question

我试图在matplotlib中的轴的末端设置一个箭头。 我不想删除刺和替换为纯箭头，因为我需要他们的功能。。。

我的实现is as slight modification of joferkington implementation

import matplotlib.pyplot as plt
import numpy as np

def arrowed_spines(ax=None, arrowLength=30, labels=('X', 'Y'), arrowStyle='<|-'):
    xlabel, ylabel = labels

    for i, spine in enumerate(['left', 'bottom']):
        # Set up the annotation parameters
        t = ax.spines[spine].get_transform()
        xy, xycoords = [1, 0], ('axes fraction', t)
        xytext, textcoords = [arrowLength, 0], ('offset points', t)

        # create arrowprops
        arrowprops = dict( arrowstyle=arrowStyle,
                           facecolor=ax.spines[spine].get_facecolor(), 
                           linewidth=ax.spines[spine].get_linewidth(),
                           alpha = ax.spines[spine].get_alpha(),
                           zorder=ax.spines[spine].get_zorder(),
                           linestyle = ax.spines[spine].get_linestyle() )

        if spine is 'bottom':
            ha, va = 'left', 'center'
            xarrow = ax.annotate(xlabel, xy, xycoords=xycoords, xytext=xytext, 
                        textcoords=textcoords, ha=ha, va='center',
                        arrowprops=arrowprops)
        else:
            ha, va = 'center', 'bottom'
            yarrow = ax.annotate(ylabel, xy[::-1], xycoords=xycoords[::-1], 
                        xytext=xytext[::-1], textcoords=textcoords[::-1], 
                        ha='center', va=va, arrowprops=arrowprops)
    return xarrow, yarrow

# plot
x = np.arange(-2., 10.0, 0.01)
plt.plot(x, x**2)
plt.gcf().set_facecolor('white')    
ax = plt.gca()
ax.set_xticks([]) 
ax.set_yticks([]) 

ax.spines['left'].set_position('center')
ax.spines['right'].set_color('none')
ax.spines['bottom'].set_position('center')
ax.spines['top'].set_color('none')

arrowed_spines(ax)

plt.show()

绘图结果显示箭头移动如下

似乎一个或两个点的移动在开始位置和箭头与脊椎的对齐上是一致的。我不知道怎么解决这个问题。任何帮助都将不胜感激。

谢谢

Answer 1

为了得到你想要的，在从arrowed_spines函数中删除以下部分之后，Julien的答案就足够了：

# removing the default axis on all sides:
for side in ['bottom','right','top','left']:
    ax.spines[side].set_visible(False)

# removing the axis ticks
plt.xticks([]) # labels 
plt.yticks([])
ax.xaxis.set_ticks_position('none') # tick markers
ax.yaxis.set_ticks_position('none')

在包含箭头之后，仍然可以修改脊椎，如您所见：

Answer 2

在这里，我结合了Julien和s3b4s的现有答案，使函数更通用，以便您可以指定要修改的轴和箭头的方向。

from matplotlib import pyplot as plt
import numpy as np

def arrowed_spines(
        ax,
        x_width_fraction=0.05,
        x_height_fraction=0.05,
        lw=None,
        ohg=0.3,
        locations=('bottom right', 'left up'),
        **arrow_kwargs
):
    """
    Add arrows to the requested spines
    Code originally sourced here: https://3diagramsperpage.wordpress.com/2014/05/25/arrowheads-for-axis-in-matplotlib/
    And interpreted here by @Julien Spronck: https://stackoverflow.com/a/33738359/1474448
    Then corrected and adapted by me for more general applications.
    :param ax: The axis being modified
    :param x_{height,width}_fraction: The fraction of the **x** axis range used for the arrow height and width
    :param lw: Linewidth. If not supplied, default behaviour is to use the value on the current left spine.
    :param ohg: Overhang fraction for the arrow.
    :param locations: Iterable of strings, each of which has the format "<spine> <direction>". These must be orthogonal
    (e.g. "left left" will result in an error). Can specify as many valid strings as required.
    :param arrow_kwargs: Passed to ax.arrow()
    :return: Dictionary of FancyArrow objects, keyed by the location strings.
    """
    # set/override some default plotting parameters if required
    arrow_kwargs.setdefault('overhang', ohg)
    arrow_kwargs.setdefault('clip_on', False)
    arrow_kwargs.update({'length_includes_head': True})

    # axis line width
    if lw is None:
        # FIXME: does this still work if the left spine has been deleted?
        lw = ax.spines['left'].get_linewidth()

    annots = {}

    xmin, xmax = ax.get_xlim()
    ymin, ymax = ax.get_ylim()

    # get width and height of axes object to compute
    # matching arrowhead length and width
    fig = ax.get_figure()
    dps = fig.dpi_scale_trans.inverted()
    bbox = ax.get_window_extent().transformed(dps)
    width, height = bbox.width, bbox.height

    # manual arrowhead width and length
    hw = x_width_fraction * (ymax-ymin)
    hl = x_height_fraction * (xmax-xmin)

    # compute matching arrowhead length and width
    yhw = hw/(ymax-ymin)*(xmax-xmin)* height/width
    yhl = hl/(xmax-xmin)*(ymax-ymin)* width/height

    # draw x and y axis
    for loc_str in locations:
        side, direction = loc_str.split(' ')
        assert side in {'top', 'bottom', 'left', 'right'}, "Unsupported side"
        assert direction in {'up', 'down', 'left', 'right'}, "Unsupported direction"

        if side in {'bottom', 'top'}:
            if direction in {'up', 'down'}:
                raise ValueError("Only left/right arrows supported on the bottom and top")

            dy = 0
            head_width = hw
            head_length = hl

            y = ymin if side == 'bottom' else ymax

            if direction == 'right':
                x = xmin
                dx = xmax - xmin
            else:
                x = xmax
                dx = xmin - xmax

        else:
            if direction in {'left', 'right'}:
                raise ValueError("Only up/downarrows supported on the left and right")
            dx = 0
            head_width = yhw
            head_length = yhl

            x = xmin if side == 'left' else xmax

            if direction == 'up':
                y = ymin
                dy = ymax - ymin
            else:
                y = ymax
                dy = ymin - ymax


        annots[loc_str] = ax.arrow(x, y, dx, dy, fc='k', ec='k', lw = lw,
                 head_width=head_width, head_length=head_length, **arrow_kwargs)

    return annots


fig = plt.figure()
ax = fig.add_subplot(111)
x = np.arange(-2., 10.0, 0.01)
ax.plot(x, x**2)
fig.set_facecolor('white')

annots = arrowed_spines(ax, locations=('bottom right', 'bottom left', 'left up', 'right down'))

plt.show()

结果：

未决问题：我试图匹配现有脊椎的线宽，但由于某些原因，箭头的线条似乎较粗。实验表明，0.8的脊椎线宽与0.3左右的箭头线宽匹配。不确定原因-当前必须将lw=<value>设置为手动修复。

Answer 3

您可以删除所有尖刺并展开箭头以覆盖数据范围（找到此代码here）：

import matplotlib.pyplot as plt
import numpy as np

def arrowed_spines(fig, ax):

    xmin, xmax = ax.get_xlim() 
    ymin, ymax = ax.get_ylim()

    # removing the default axis on all sides:
    for side in ['bottom','right','top','left']:
        ax.spines[side].set_visible(False)

    # removing the axis ticks
    plt.xticks([]) # labels 
    plt.yticks([])
    ax.xaxis.set_ticks_position('none') # tick markers
    ax.yaxis.set_ticks_position('none')

    # get width and height of axes object to compute 
    # matching arrowhead length and width
    dps = fig.dpi_scale_trans.inverted()
    bbox = ax.get_window_extent().transformed(dps)
    width, height = bbox.width, bbox.height

    # manual arrowhead width and length
    hw = 1./20.*(ymax-ymin) 
    hl = 1./20.*(xmax-xmin)
    lw = 1. # axis line width
    ohg = 0.3 # arrow overhang

    # compute matching arrowhead length and width
    yhw = hw/(ymax-ymin)*(xmax-xmin)* height/width 
    yhl = hl/(xmax-xmin)*(ymax-ymin)* width/height

    # draw x and y axis
    ax.arrow(xmin, 0, xmax-xmin, 0., fc='k', ec='k', lw = lw, 
             head_width=hw, head_length=hl, overhang = ohg, 
             length_includes_head= True, clip_on = False) 

    ax.arrow(0, ymin, 0., ymax-ymin, fc='k', ec='k', lw = lw, 
             head_width=yhw, head_length=yhl, overhang = ohg, 
             length_includes_head= True, clip_on = False)


# plot
x = np.arange(-2., 10.0, 0.01)
plt.plot(x, x**2)
fig = plt.gcf()
fig.set_facecolor('white') 
ax = plt.gca()

arrowed_spines(fig, ax)

plt.show()