pandas Python中的石斑鱼和轴的长度必须相同
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Grouper and axis must be same length in Python
提问by Rowling
I am a beginner of Python, and I study a textbook to learn the Pandas module. I have a dataframe called Berri_bike, and it is from the following code:
我是 Python 的初学者，我正在学习一本教科书来学习 Pandas 模块。我有一个名为 Berri_bike 的数据框，它来自以下代码：
bike_df=pd.read_csv(os.path.join(path,'comptagevelo2012.csv'),parse_dates=['Date'],\
encoding='latin1',dayfirst=True,index_col='Date')
Berri_bike=bike_df['Berri1'].copy() # get only the column='Berri1'
Berri_bike['Weekday']=Berri_bike.index.weekday
weekday_counts = Berri_bike.groupby('Weekday').aggregate(sum)
weekday_counts
I have 3 columns in my Berri_bilk , a data index- from 1/1/2012 to 12/31/2012, and value column with numbers for each data, and a weekday column I assigned to it. But when I want to group by the values, I got the error: ValueError: Grouper and axis must be same length, I am not sure what this mean, what I want to do is very simple, like in SQL, sum(value) grouped weekday... can anyone please let me know what happended here?
我的 Berri_bilk 中有 3 列，一个数据索引 - 从 1/1/2012 到 12/31/2012，以及每个数据带有数字的值列，以及我分配给它的工作日列。但是当我想按值分组时，出现错误：ValueError: Grouper and axis must be same length，我不确定这是什么意思，我想做的很简单，就像在 SQL 中一样，sum(value)工作日分组...谁能告诉我这里发生了什么？
回答by Mr. T
You copy your column into a pandas series instead of a new dataframe, hence the following operations behave differently. You can see this if you print out Berri_bikebecause it doesn't show the column name.
Instead, you should copy the column into a new dataframe:
您将列复制到 Pandas 系列而不是新数据帧中，因此以下操作的行为有所不同。如果您打印出来，您可以看到这一点，Berri_bike因为它没有显示列名。
相反，您应该将该列复制到一个新的数据框中：
import pandas as pd
df = pd.DataFrame(np.random.randint(0, 30, size = (70, 2)),
columns = ["A", "B"],
index = pd.date_range("20180101", periods = 70))
Berri_bike = df[["A"]]
Berri_bike['Weekday'] = Berri_bike.index.weekday
weekday_counts = Berri_bike.groupby("Weekday").sum()
print(weekday_counts)
#sample output
A
Weekday
0 148
1 101
2 127
3 139
4 163
5 74
6 135
