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Examples

In [1]:
import numpy as np
import pandas as pd
In [2]:
s = pd.Series(range(6))
s.where(s > 0)
Out[2]:
0    NaN
1    1.0
2    2.0
3    3.0
4    4.0
5    5.0
dtype: float64
In [3]:
s.mask(s > 0)
Out[3]:
0    0.0
1    NaN
2    NaN
3    NaN
4    NaN
5    NaN
dtype: float64
In [4]:
s.where(s > 1, 10)
Out[4]:
0    10
1    10
2     2
3     3
4     4
5     5
dtype: int64
In [5]:
df = pd.DataFrame(np.arange(10).reshape(-1, 2), columns=['P', 'Q'])
df
Out[5]:
P Q
0 0 1
1 2 3
2 4 5
3 6 7
4 8 9
In [6]:
m = df % 3 == 0
df.where(m, -df)
Out[6]:
P Q
0 0 -1
1 -2 3
2 -4 -5
3 6 -7
4 -8 9
In [7]:
df.where(m, -df) == np.where(m, df, -df)
Out[7]:
P Q
0 True True
1 True True
2 True True
3 True True
4 True True
In [8]:
df.where(m, -df) == df.mask(~m, -df)
Out[8]:
P Q
0 True True
1 True True
2 True True
3 True True
4 True True