pandas 如何获取熊猫中的每第 n 列？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/35928533/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
How to get every nth column in pandas?
提问by Angelo
I have a dataframe which looks like this:
我有一个如下所示的数据框：
a1 b1 c1 a2 b2 c2 a3 ...
x 1.2 1.3 1.2 ... ... ... ...
y 1.4 1.2 ... ... ... ... ...
z ...
What I want is grouping by every nth column. In other words, I want a dataframe with all the as, one with bs and one with cs
我想要的是按每第 n 列分组。换句话说，我想要一个包含所有 as 的数据框，一个包含 bs，一个包含 cs
a1 a2 a4
x 1.2 ... ...
y
z
In another SO question I saw that is possibile to do df.iloc[::5,:], for example, to get every 5th raw. I could do of course df.iloc[:,::3]to get the c cols but it doesn't work for getting a and b.
在另一个 SO 问题中，我看到这是可能的df.iloc[::5,:]，例如，每 5 次获取原始数据。我当然df.iloc[:,::3]可以得到 c cols，但它不适用于获取 a 和 b。
Any ideas?
有任何想法吗？
回答by EdChum
slice the columns:
切片列：
df[df.columns[::2]]
To get every nth column
获取每第 n 列
Example:
例子：
In [2]:
cols = ['a1','b1','c1','a2','b2','c2','a3']
df = pd.DataFrame(columns=cols)
df
Out[2]:
Empty DataFrame
Columns: [a1, b1, c1, a2, b2, c2, a3]
Index: []
In [3]:
df[df.columns[::3]]
Out[3]:
Empty DataFrame
Columns: [a1, a2, a3]
Index: []
You can also filter using startswith:
您还可以使用过滤器startswith：
In [5]:
a = df.columns[df.columns.str.startswith('a')]
df[a]
Out[5]:
Empty DataFrame
Columns: [a1, a2, a3]
Index: []
and do the same for b cols and c cols etc..
并对 b cols 和 c cols 等执行相同的操作。
You can get a set of all the unique col prefixes using the following:
您可以使用以下命令获取一组所有唯一 col 前缀：
In [19]:
df.columns.str.extract(r'([a-zA-Z])').unique()
Out[19]:
array(['a', 'b', 'c'], dtype=object)
You can then use these values to filter the columns using startswith
然后，您可以使用这些值来过滤列 startswith
回答by divandc
The following should work:
以下应该工作：
df.ix[:, ::2] - get every second column, beginning with first (here all a's)
df.ix[:, 1::2] - get every second column, beginning with second (b's)
....
I just searched for a solution to the same problem and that solved it.
我只是搜索了相同问题的解决方案，并解决了它。
回答by joctee
In current version (0.24), this works:
在当前版本 (0.24) 中，这有效：
Getting your 'a' columns:
获取您的“a”列：
df.iloc[:, ::3]
getting your 'b' columns:
获取您的“b”列：
df.iloc[:, 1::3]
getting your 'c' columns:
获取您的“c”列：
df.iloc[:, 2::3]
