[英]How to create categorical variable based on a numerical variable
My DataFrame hase one column:我的 DataFrame 有一列:
import pandas as pd
list=[1,1,4,5,6,6,30,20,80,90]
df=pd.DataFrame({'col1':list})
How can I add one more column 'col2' that would contain categorical information in reference to col1:如何再添加一列“col2”,该列将包含参考 col1 的分类信息:
if col1 > 0 and col1 <= 10 then col2 = 'xxx'
if col1 > 10 and col1 <= 50 then col2 = 'yyy'
if col1 > 50 then col2 = 'zzz'
You could first create a new column col2
, and update its values based on the conditions:您可以首先创建一个新列col2
,并根据条件更新其值:
df['col2'] = 'zzz'
df.loc[(df['col1'] > 0) & (df['col1'] <= 10), 'col2'] = 'xxx'
df.loc[(df['col1'] > 10) & (df['col1'] <= 50), 'col2'] = 'yyy'
print df
Output:输出:
col1 col2
0 1 xxx
1 1 xxx
2 4 xxx
3 5 xxx
4 6 xxx
5 6 xxx
6 30 yyy
7 20 yyy
8 80 zzz
9 90 zzz
Alternatively, you can also apply a function based on the column col1
:或者,您还可以应用基于列col1
的函数:
def func(x):
if 0 < x <= 10:
return 'xxx'
elif 10 < x <= 50:
return 'yyy'
return 'zzz'
df['col2'] = df['col1'].apply(func)
and this will result in the same output.这将导致相同的输出。
The apply
approach should be preferred in this case as it is much faster:在这种情况下应该首选apply
方法,因为它要快得多:
%timeit run() # packaged to run the first approach
# 100 loops, best of 3: 3.28 ms per loop
%timeit df['col2'] = df['col1'].apply(func)
# 10000 loops, best of 3: 187 µs per loop
However, when the size of the DataFrame is large, the built-in vectorized operations (ie with the masking approach) might be faster.但是,当 DataFrame 的大小很大时,内置的矢量化操作(即使用掩码方法)可能会更快。
2 ways, use a couple loc
calls to mask the rows where the conditions are met: 2 种方式,使用几个loc
调用来屏蔽满足条件的行:
In [309]:
df.loc[(df['col1'] > 0) & (df['col1']<= 10), 'col2'] = 'xxx'
df.loc[(df['col1'] > 10) & (df['col1']<= 50), 'col2'] = 'yyy'
df.loc[df['col1'] > 50, 'col2'] = 'zzz'
df
Out[309]:
col1 col2
0 1 xxx
1 1 xxx
2 4 xxx
3 5 xxx
4 6 xxx
5 6 xxx
6 30 yyy
7 20 yyy
8 80 zzz
9 90 zzz
Or use a nested np.where
:或者使用嵌套的np.where
:
In [310]:
df['col2'] = np.where((df['col1'] > 0) & (df['col1']<= 10), 'xxx', np.where((df['col1'] > 10) & (df['col1']<= 50), 'yyy', 'zzz'))
df
Out[310]:
col1 col2
0 1 xxx
1 1 xxx
2 4 xxx
3 5 xxx
4 6 xxx
5 6 xxx
6 30 yyy
7 20 yyy
8 80 zzz
9 90 zzz
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