Python 当列名是整数时，按列号索引 Pandas DataFrame
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Index pandas DataFrame by column numbers, when column names are integers
提问by Akavall
I am trying to keep just certain columns of a DataFrame, and it works fine when column names are strings:
我试图只保留 DataFrame 的某些列，当列名是字符串时它工作正常：
In [2]: import numpy as np
In [3]: import pandas as pd
In [4]: a = np.arange(35).reshape(5,7)
In [5]: df = pd.DataFrame(a, ['x', 'y', 'u', 'z', 'w'], ['a', 'b', 'c', 'd', 'e', 'f', 'g'])
In [6]: df
Out[6]:
a b c d e f g
x 0 1 2 3 4 5 6
y 7 8 9 10 11 12 13
u 14 15 16 17 18 19 20
z 21 22 23 24 25 26 27
w 28 29 30 31 32 33 34
[5 rows x 7 columns]
In [7]: df[[1,3]] #No problem
Out[7]:
b d
x 1 3
y 8 10
u 15 17
z 22 24
w 29 31
However, when column names are integers, I am getting a key error:
但是，当列名是整数时，我收到一个关键错误：
In [8]: df = pd.DataFrame(a, ['x', 'y', 'u', 'z', 'w'], range(10, 17))
In [9]: df
Out[9]:
10 11 12 13 14 15 16
x 0 1 2 3 4 5 6
y 7 8 9 10 11 12 13
u 14 15 16 17 18 19 20
z 21 22 23 24 25 26 27
w 28 29 30 31 32 33 34
[5 rows x 7 columns]
In [10]: df[[1,3]]
Results in:
结果是：
KeyError: '[1 3] not in index'
I can see why pandas does not allow that -> to avoid mix up between indexing by column names and column numbers. However, is there a way to tell pandas that I want to index by column numbers? Of course, one solution is to convert column names to strings, but I am wondering if there is a better solution.
我可以理解为什么 Pandas 不允许这样做 -> 以避免在按列名和列号进行索引之间混淆。但是，有没有办法告诉熊猫我想按列号索引？当然，一种解决方案是将列名转换为字符串，但我想知道是否有更好的解决方案。
采纳答案by Jeff
回答by JD Long
This is certainly one of those things that feels like a bug but is really a design decision (I think).
这当然是感觉像错误但实际上是设计决策的事情之一（我认为）。
A few work around options:
一些解决选项：
rename the columns with their positions as their name:
用它们的位置作为名称重命名列：
df.columns = arange(0,len(df.columns))
Another way is to get names from df.columns:
另一种方法是从df.columns以下位置获取名称：
print df[ df.columns[[1,3]] ]
11 13
x 1 3
y 8 10
u 15 17
z 22 24
w 29 31
I suspect this is the most appealing as it just requires adding a wee bit of code and not changing any column names.
我怀疑这是最吸引人的，因为它只需要添加一点代码而不更改任何列名。
