在matplotlib中设置分组条形图之间的间距

Question

我正在尝试在matplotlib中创建一个分组的条形图,遵循库中的示例.我使用以下内容:

import matplotlib.pyplot as plt
plt.figure(figsize=(7,7), dpi=300)
xticks = [0.1, 1.1]
groups = [[1.04, 0.96],
          [1.69, 4.02]]
group_labels = ["G1", "G2"]
num_items = len(group_labels)
ind = arange(num_items)
width = 0.1
s = plt.subplot(1,1,1)
for num, vals in enumerate(groups):
    print "plotting: ", vals
    group_len = len(vals)
    gene_rects = plt.bar(ind, vals, width,
                         align="center")
    ind = ind + width
num_groups = len(group_labels)
# Make label centered with respect to group of bars
# Is there a less complicated way?
offset = (num_groups / 2.) * width
xticks = arange(num_groups) + offset
s.set_xticks(xticks)
print "xticks: ", xticks
plt.xlim([0 - width, max(xticks) + (num_groups * width)])
s.set_xticklabels(group_labels)

我的问题是:

1. 如何控制各组条之间的空间？现在间距很大,看起来很傻.请注意,我不想让条形更宽 - 我希望它们具有相同的宽度,但是要靠得更近.

2. 如何让标签在条形组下方居中？我试图想出一些算术计算来将xlabels定位在正确的位置(参见上面的代码),但它仍然稍微偏离......感觉有点像编写绘图库而不是使用一个.怎么解决这个问题？(matplotlib是否有一个包装器或内置实用程序,这是默认行为？)

编辑:回复@mlgill:谢谢你的回答.您的代码肯定更优雅,但仍然存在相同的问题,即条的宽度和组之间的间距不是单独控制的.你的图表看起来是正确的,但条形图太宽了 - 它看起来像一个Excel图形 - 我想让条形更薄.

现在链接宽度和边距,所以如果我尝试:

margin = 0.60
width = (1.-2.*margin)/num_items

这使得酒吧更加苗条,但让这群人相距甚远,所以情节再次看起来并不合适.

如何创建一个带有两个参数的分组条形图函数:每个条形图的宽度,条形图组之间的间距,以及正确编写代码的图形,即x轴标签位于组的下方？

我认为,由于用户必须计算特定的低级布局数量,如边距和宽度,我们仍然基本上编写绘图库:)

Answer 1

两个问题的诀窍是要理解Matplotlib中的条形图表示每个系列(G1,G2)的总宽度为"1.0",计算两侧的边距.因此,最简单的方法是设置边距,然后计算每个柱的宽度,具体取决于每个系列中有多少个.在您的情况下,每个系列有两个条.

假设你左对齐每个条,而不是像你一样对齐它们,这个设置将导致系列在x轴上跨越0.0到1.0,1.0到2.0,依此类推.因此,每个系列的确切中心(您希望标签出现的位置)将为0.5,1.5等.

我已经清理了你的代码,因为有很多无关的变量.见其中的评论.

import matplotlib.pyplot as plt
import numpy as np

plt.figure(figsize=(7,7), dpi=300)

groups = [[1.04, 0.96],
          [1.69, 4.02]]
group_labels = ["G1", "G2"]
num_items = len(group_labels)
# This needs to be a numpy range for xdata calculations
# to work.
ind = np.arange(num_items)

# Bar graphs expect a total width of "1.0" per group
# Thus, you should make the sum of the two margins
# plus the sum of the width for each entry equal 1.0.
# One way of doing that is shown below. You can make
# The margins smaller if they're still too big.
margin = 0.05
width = (1.-2.*margin)/num_items

s = plt.subplot(1,1,1)
for num, vals in enumerate(groups):
    print "plotting: ", vals
    # The position of the xdata must be calculated for each of the two data series
    xdata = ind+margin+(num*width)
    # Removing the "align=center" feature will left align graphs, which is what
    # this method of calculating positions assumes
    gene_rects = plt.bar(xdata, vals, width)


# You should no longer need to manually set the plot limit since everything 
# is scaled to one.
# Also the ticks should be much simpler now that each group of bars extends from
# 0.0 to 1.0, 1.0 to 2.0, and so forth and, thus, are centered at 0.5, 1.5, etc.
s.set_xticks(ind+0.5)
s.set_xticklabels(group_labels)

Answer 2

其实我觉得这个问题是通过调整最佳的解决figsize和width; 这是我的输出figsize=(2,7)和width=0.3:

顺便说一句,这种类型的东西变得很多,如果你使用更简单的pandas包装(我也是进口的seaborn,没有必要的解决方案,但让剧情有很多漂亮和更现代的看着在我看来):

import pandas as pd        
import seaborn 
seaborn.set() 

df = pd.DataFrame(groups, index=group_labels)
df.plot(kind='bar', legend=False, width=0.8, figsize=(2,5))
plt.show()