装箱后无法访问数据框的 groupby 对象的各个列

Question

这个问题与this one 类似，但有一个关键区别 - 链接问题的解决方案不能解决数据框分组到 bin 时的问题。

以下用于箱线图绘制 2 个变量的 bin 的相对分布的代码会产生错误：

import pandas as pd
import seaborn as sns

raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks', 'Dragoons', 'Dragoons', 'Dragoons', 'Dragoons', 'Scouts', 'Scouts', 'Scouts', 'Scouts'], 
        'company': ['1st', '1st', '2nd', '2nd', '1st', '1st', '2nd', '2nd','1st', '1st', '2nd', '2nd'], 
        'name': ['Miller', 'Jacobson', 'Ali', 'Milner', 'Cooze', 'Jacon', 'Ryaner', 'Sone', 'Sloan', 'Piger', 'Riani', 'Ali'], 
        'preTestScore': [4, 24, 31, 2, 3, 4, 24, 31, 2, 3, 2, 3],
        'postTestScore': [25, 94, 57, 62, 70, 25, 94, 57, 62, 70, 62, 70]}
df = pd.DataFrame(raw_data, columns = ['regiment', 'company', 'name', 'preTestScore', 'postTestScore'])


df1 = df.groupby(['regiment'])['preTestScore'].value_counts().unstack()
df1.fillna(0, inplace=True)


sns.boxplot(x='regiment', y='preTestScore', data=df1)

---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-241-fc8036eb7d0b> in <module>()
----> 1 sns.boxplot(x='regiment', y='preTestScore', data=df1)

~\AppData\Local\Continuum\anaconda3\lib\site-packages\seaborn\categorical.py in boxplot(x, y, hue, data, order, hue_order, orient, color, palette, saturation, width, dodge, fliersize, linewidth, whis, notch, ax, **kwargs)
   2209     plotter = _BoxPlotter(x, y, hue, data, order, hue_order,
   2210                           orient, color, palette, saturation,
-> 2211                           width, dodge, fliersize, linewidth)
   2212 
   2213     if ax is None:

~\AppData\Local\Continuum\anaconda3\lib\site-packages\seaborn\categorical.py in __init__(self, x, y, hue, data, order, hue_order, orient, color, palette, saturation, width, dodge, fliersize, linewidth)
    439                  width, dodge, fliersize, linewidth):
    440 
--> 441         self.establish_variables(x, y, hue, data, orient, order, hue_order)
    442         self.establish_colors(color, palette, saturation)
    443 

~\AppData\Local\Continuum\anaconda3\lib\site-packages\seaborn\categorical.py in establish_variables(self, x, y, hue, data, orient, order, hue_order, units)
    149                 if isinstance(input, string_types):
    150                     err = "Could not interpret input '{}'".format(input)
--> 151                     raise ValueError(err)
    152 
    153             # Figure out the plotting orientation

ValueError: Could not interpret input 'regiment'

如果我删除 x 和 y 参数，它会生成一个箱线图，但它不是我想要的：

我该如何解决这个问题？我尝试了以下方法：

df1 = df.groupby(['regiment'])['preTestScore'].value_counts().unstack()
df1.fillna(0, inplace=True)
df1 = df1.reset_index()
df1

它现在看起来像一个数据框，所以我想提取这个数据框的列名并按顺序为每个列绘制：

cols = df1.columns[1:len(df1.columns)]
for i in range(len(cols)):
    sns.boxplot(x='regiment', y=cols[i], data=df1)

这看起来不对。事实上，这不是一个正常的数据帧；如果我们打印出它的列，它不会将 regiment 显示为列，这就是 boxplot 给出错误 ValueError: Could not interpret input 'regiment' 的原因：

df1.columns
>>> Index(['regiment', 2, 3, 4, 24, 31], dtype='object', name='preTestScore')

所以，如果我能以某种方式使regiment 成为数据框的一列，我想我应该能够绘制preTestScore 与regiment 的箱线图。我错了吗？

---

编辑：我想要的是这样的：

df1 = df.groupby(['regiment'])['preTestScore'].value_counts().unstack()
df1.fillna(0, inplace=True)

# This df2 dataframe is the one I'm trying to construct using groupby
data = {'regiment':['Dragoons', 'Nighthawks', 'Scouts'], 'preTestScore 2':[0.0, 1.0, 2.0], 'preTestScore 3':[1.0, 0.0, 2.0],
        'preTestScore 4':[1.0, 1.0, 0.0], 'preTestScore 24':[1.0, 1.0, 0.0], 'preTestScore 31':[1.0, 1.0, 0.0]}

cols = ['regiment', 'preTestScore 2', 'preTestScore 3', 'preTestScore 4', 'preTestScore 24', 'preTestScore 31']

df2 = pd.DataFrame(data, columns=cols)
df2

fig = plt.figure(figsize=(20,3))

count = 1
for col in cols[1:]:
    plt.subplot(1, len(cols)-1, count)
    sns.boxplot(x='regiment', y=col, data=df2)
    count+=1

Answer 1

如果你对你的数据框df1 执行reset_index()，你应该得到你想要的数据框。

问题是您有一个所需的列 (regiment) 作为索引，因此您需要重置它并使其成为另一列。

编辑：添加add_prefix 以获得结果数据框中的正确列名

示例代码：

import pandas as pd
import seaborn as sns
import matplotlib.pyplot as plt

raw_data = {'regiment': ['Nighthawks', 'Nighthawks', 'Nighthawks', 'Nighthawks', 'Dragoons', 'Dragoons', 'Dragoons', 'Dragoons', 'Scouts', 'Scouts', 'Scouts', 'Scouts'], 
        'company': ['1st', '1st', '2nd', '2nd', '1st', '1st', '2nd', '2nd','1st', '1st', '2nd', '2nd'], 
        'name': ['Miller', 'Jacobson', 'Ali', 'Milner', 'Cooze', 'Jacon', 'Ryaner', 'Sone', 'Sloan', 'Piger', 'Riani', 'Ali'], 
        'preTestScore': [4, 24, 31, 2, 3, 4, 24, 31, 2, 3, 2, 3],
        'postTestScore': [25, 94, 57, 62, 70, 25, 94, 57, 62, 70, 62, 70]}
df = pd.DataFrame(raw_data, columns = ['regiment', 'company', 'name', 'preTestScore', 'postTestScore'])


df1 = df.groupby(['regiment'])['preTestScore'].value_counts().unstack()
df1.fillna(0, inplace=True)

df1 = df1.add_prefix('preTestScore ')  # <- add_prefix for proper column names

df2 = df1.reset_index()  # <- Here is reset_index()
cols = df2.columns

fig = plt.figure(figsize=(20,3))

count = 1
for col in cols[1:]:
    plt.subplot(1, len(cols)-1, count)
    sns.boxplot(x='regiment', y=col, data=df2)
    count+=1

输出：