如何去除单张图表中多个colorbar之间的空白区域

问题描述 #

我尝试在Matplotlib中水平绘制三个colorbar，希望消除它们之间的空白区域，请问是否有实现该需求或逐步调整间距的方法？

复现代码 #

import matplotlib as mpl
import matplotlib.pyplot as plt

fig, axes = plt.subplots(figsize=(8, 2), nrows=3, ncols=1, sharex=True, sharey=True)
fig.suptitle('Bar comparison')

# upper colorbar
bar1 = [['a', 0, 0.6], ['b', 0.6, 1.2], ['a', 1.2, 1.8], ['b', 1.8, 4]]
colors1 = ['yellow', 'blue', 'yellow', 'blue']
cmap1 = mpl.colors.ListedColormap(colors1)
bounds1 = [0] + [i[2] for i in bar1]
norm1 = mpl.colors.BoundaryNorm(bounds1, len(colors1))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap1, norm=norm1),
    cax=axes[0],
    ticks=[[0], [bar1[-1][2]]],
    spacing='proportional',
    orientation='horizontal')

# middle colorbar
bar2 = [['a', 0, 0.5], ['b', 0.5, 1], ['a', 1, 2], ['b', 2, 3.8], ['a', 3.8, 4]]
colors2 = ['yellow', 'blue', 'yellow', 'blue', 'yellow']
cmap2 = mpl.colors.ListedColormap(colors2)
bounds2 = [0] + [i[2] for i in bar2]
norm2 = mpl.colors.BoundaryNorm(bounds2, len(colors2))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap2, norm=norm2),
    cax=axes[1],
    ticks=[[0], [bar2[-1][2]]], 
    spacing='proportional',
    orientation='horizontal')

# lower colorbar
bar3 = [['a', 0, 0.5], ['b', 0.5, 1], ['a', 1, 2], ['b', 2, 3.8], ['a', 3.8, 4]]
colors3 = ['green', 'green', 'green', 'green', 'red']
cmap3 = mpl.colors.ListedColormap(colors3)
bounds3 = [0] + [i[2] for i in bar3]
norm3 = mpl.colors.BoundaryNorm(bounds3, len(colors3))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap3, norm=norm3),
    cax=axes[2],
    ticks=[[0], [bar3[-1][2]]],
    spacing='proportional',
    orientation='horizontal')

# Figure settings
# Hide x labels and tick labels for all but bottom plot.
for ax in axes:
    ax.label_outer()
plt.show()

解决方案 #

方法一：直接消除子图间距（推荐） #

通过设置子图垂直间距为0，并清理轴上冗余元素，让三个colorbar紧密贴合。修改后的代码如下：

import matplotlib as mpl
import matplotlib.pyplot as plt

# 关键：设置hspace=0消除子图间垂直空白
fig, axes = plt.subplots(figsize=(8, 2), nrows=3, ncols=1, sharex=True, sharey=True, gridspec_kw={'hspace': 0})
fig.suptitle('Bar comparison')

# upper colorbar
bar1 = [['a', 0, 0.6], ['b', 0.6, 1.2], ['a', 1.2, 1.8], ['b', 1.8, 4]]
colors1 = ['yellow', 'blue', 'yellow', 'blue']
cmap1 = mpl.colors.ListedColormap(colors1)
bounds1 = [0] + [i[2] for i in bar1]
norm1 = mpl.colors.BoundaryNorm(bounds1, len(colors1))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap1, norm=norm1),
    cax=axes[0],
    ticks=[0, bar1[-1][2]],  # 修复嵌套列表导致的刻度异常
    spacing='proportional',
    orientation='horizontal')

# middle colorbar
bar2 = [['a', 0, 0.5], ['b', 0.5, 1], ['a', 1, 2], ['b', 2, 3.8], ['a', 3.8, 4]]
colors2 = ['yellow', 'blue', 'yellow', 'blue', 'yellow']
cmap2 = mpl.colors.ListedColormap(colors2)
bounds2 = [0] + [i[2] for i in bar2]
norm2 = mpl.colors.BoundaryNorm(bounds2, len(colors2))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap2, norm=norm2),
    cax=axes[1],
    ticks=[0, bar2[-1][2]],
    spacing='proportional',
    orientation='horizontal')

# lower colorbar
bar3 = [['a', 0, 0.5], ['b', 0.5, 1], ['a', 1, 2], ['b', 2, 3.8], ['a', 3.8, 4]]
colors3 = ['green', 'green', 'green', 'green', 'red']
cmap3 = mpl.colors.ListedColormap(colors3)
bounds3 = [0] + [i[2] for i in bar3]
norm3 = mpl.colors.BoundaryNorm(bounds3, len(colors3))
plt.colorbar(mpl.cm.ScalarMappable(cmap=cmap3, norm=norm3),
    cax=axes[2],
    ticks=[0, bar3[-1][2]],
    spacing='proportional',
    orientation='horizontal')

# 清理轴元素，避免额外空白
for ax in axes:
    ax.label_outer()
    ax.margins(y=0)  # 移除y方向的边距
    # 隐藏不需要的边框和刻度
    ax.set_yticks([])
    for spine in ax.spines.values():
        spine.set_visible(False)

plt.show()

方法二：精细调整间距 #

如果不需要完全消除空白，而是自定义间距大小，可以在plt.show()前添加以下代码，数值越小间距越小：

fig.subplots_adjust(hspace=0.05)  # 设置0.05的小间距，可根据需求修改

关键说明 #

1. gridspec_kw={'hspace': 0}：直接让子图间垂直间距为0，是消除空白的核心设置。
2. 清理轴元素：colorbar的容器轴不需要y轴刻度、边框，隐藏这些元素并设置y边距为0，避免轴本身带来额外空白。
3. 修复刻度设置：原代码中ticks用嵌套列表会导致显示异常，改为普通列表[0, bar[-1][2]]更合理。

内容的提问来源于stack exchange，提问作者lonyen11