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使用两个轴打印时,如何填充图例背景色?

multiple-axes fill legend matplotlib python

Cebbie · 技术社区 · 8 年前

问题

我有一个有两个y轴的图,每个y轴对应一组线。实线对应于左y轴,虚线对应于右y轴。我也有一个传说,我只想用它实线

问题是当我为实线绘制图例,然后为虚线绘制代码时,网格线通过图例显示。我需要为两个轴指定网格线,因为它们不会以其他方式显示,如果我将图例移动到虚线,它将使用虚线作为关键点。我也不想改变我的绘图顺序。

代码和绘图

#Plot
x= np.arange(0,3)
fig,ax = plt.subplots(figsize=(6,6))
#DOD
dod1 = ax.plot(x, ctrl_dod,  color='r',       label='CTRL'  )
dod2 = ax.plot(x, mfkc_dod,  color='#e68a00', label='MFKC'  )
dod3 = ax.plot(x, gses_dod,  color='green',   label='GSES'  )
dod4 = ax.plot(x, gses3_dod, color='blue',    label='GSES-3')
dod5 = ax.plot(x, gses4_dod, color='purple',  label='GSES-4')
dod6 = ax.plot(x, mera_dod,  color='brown',   label='MERRA2')
ax.xaxis.grid(True)
ax.set_ylim([0.02,0.044])
ax.set_yticks(np.arange(0.02,0.045,0.004))
ax.set_xlabel('Month')
ax.set_ylabel('Dust Optical Depth (550 nm)')
ax.set_title('Global Mean DOD and DCM')
legend = ax.legend()
legend.get_frame().set_facecolor('white')

#DCM
ax2  = ax.twinx()
dcm1 = ax2.plot(x, ctrl_dcm*1e6,  color='r',       linestyle='--', label='CTRL'  )
dcm2 = ax2.plot(x, mfkc_dcm*1e6,  color='#e68a00', linestyle='--', label='MFKC'  )
dcm3 = ax2.plot(x, gses_dcm*1e6,  color='green',   linestyle='--', label='GSES'  )
dcm4 = ax2.plot(x, gses3_dcm*1e6, color='blue',    linestyle='--', label='GSES-3')
dcm5 = ax2.plot(x, gses4_dcm*1e6, color='purple',  linestyle='--', label='GSES-4')
dcm6 = ax2.plot(x, mera_dcm*1e6,  color='brown',   linestyle='--', label='MERRA2')
ax2.xaxis.grid(True)
ax2.yaxis.grid(True)
ax2.set_xlabel('Month')
ax2.set_ylabel('Dust Column Mass (mg m-2)')

#Limits
axes = plt.gca()
axes.set_xlim([-0.25,2.25])

#Labels
axes.set_xticks(x)
axes.set_xticklabels(['June','July','August'])

#Save
pylab.savefig('dod+dcm.png')

我怎么能

b) 图例的背景是白色的吗?

2 回复 | 直到 8 年前

ImportanceOfBeingErnest 8 年前

您可以为第二个轴创建图例,但使用第一个轴的控制柄。

h, l = ax.get_legend_handles_labels()
legend = ax2.legend(h,l, facecolor="white")

Bastian 4 年前

我来到这里,因为我有同样的问题,但想要两个独立的传说,每一个双轴一个。

@ImportanceOfBeingErnest提供的公认答案不再有效,因为它只允许将一个图例附加到 ax2

https://github.com/matplotlib/matplotlib/issues/3706#issuecomment-378407795 .

我将它们都转换为一个函数,我通常在本例中使用这个函数,并认为在这里提供它会很有用:

def legend_to_ax( ax, ax_placein=None, method=2, **kwargs ):
    """ Wrapper around ax.legend(**kwargs) which permits to have the legend
    placed in the axis ax_placein.
    This is useful when drawing legends for multiple axes, e.g.produced with
    ax2 = ax1.twinx(), in order to have all legends on top of all axes.
    In this case provide the uppermost axis, e.g. ax2 here, as ax_placein.
    Args:
     - ax         : axis for which the legend is created
     - ax_placein : axis which the legend should be placed in (optional)
     - method     : method by which to handle the placement of the legend in
                    ax_placein.
                    method=1 ... based on 
                                 https://stackoverflow.com/a/45336414/7042795
                                 This method fails when multiple legends should
                                 be added to ax_placein.
                    method=2 ... based on
                                 https://github.com/matplotlib/matplotlib/issues/3706#issuecomment-378407795
                                 This adds the legend as an artist to ax_placein
                                 making it no longer appear via ax.get_legend().
                                 Instead parse ax_placein.artists()
     - **kwargs   : kwargs of ax.legend()
    Returns:
     - leg        : legend handle
    """

    if ax_placein is None:
        leg = ax.legend(**kwargs)
    
    elif method==1:
        # based on https://stackoverflow.com/a/45336414/7042795
        h, l = ax.get_legend_handles_labels()
        if ax_placein is not None:
            ax = ax_placein
        leg =  ax.legend( h, l, **kwargs)
    
    elif method==2:
        # based on https://github.com/matplotlib/matplotlib/issues/3706#issuecomment-378407795
        leg = ax.legend(**kwargs)
        if ax_placein is not None:
            leg.remove()
            ax_placein.add_artist(leg)
    
    return leg

因此,使用此函数,您可以简单地执行以下操作

legend = legend_to_ax( ax, ax_placein=ax2, method=1, facecolor="white")

或

legend = legend_to_ax( ax, ax_placein=ax2, method=2, facecolor="white")

legend1 = legend_to_ax( ax,  ax_placein=ax2, method=2, facecolor="white", loc="upper left")
legend2 = legend_to_ax( ax2, ax_placein=ax2, method=2, facecolor="white", loc="upper right")