Filtering Pandas Dataframe Results without saving to a variable first

Question

Is there a way to more efficiently filter a result on a data frame without having to explicitly save it in a variable and then filter? For instance, in the code below I would like to add something to line 3 to be able to achieve either df1 or df2.

import pandas as pd
df=pd.DataFrame({'A' : [1,2,3,4,5], 'B' : [0,0,0,0,0]})
df=df.var()
df1 = df[df!=0]
df2 = df[df > 3]

Answer 1

If you want to filter Pandas Series "on the fly", you can use .loc[] indexer in conjunction with the callable method (for example using lambda function).

Demo:

In [8]: df.var()
Out[8]:
A    2.5
B    0.0
dtype: float64

In [9]: df.var().loc[lambda ser: ser!=0]
Out[9]:
A    2.5
dtype: float64

In [10]: df.var().loc[lambda ser: ser>3]
Out[10]: Series([], dtype: float64)

If you want to filter a DataFrame, then you can use DF.query(...) method:

In [11]: df
Out[11]:
   A  B
0  1  0
1  2  0
2  3  0
3  4  0
4  5  0

In [12]: df.query("A >= 3")
Out[12]:
   A  B
2  3  0
3  4  0
4  5  0

Answer 2

I believe you are looking for this:

import pandas as pd
df=pd.DataFrame({'A' : [1,2,3,4,5], 'B' : [0,0,0,0,0]})
df1 = df[df['B'] != 0]
df2 = df[df['A'] > 3]

Depending on what you are trying to accomplish, you can modify this to meet your needs.