using variable to filter rows in pandas dataframe-CodePudding

I have dataframe defined as below and want to filter using variable name ft as in below code:

df = pd.DataFrame([[1,2], [3,4]], columns=['a', 'b'])

ft=["a"]

dt=df[df[ft]==3]

print(dt)

I get below result:

a   b

NaN NaN

3.0 NaN

while actual result should have been only 2nd row

 a  b

 3  4

I dont want to use column name, but variable.

thanks in advance for any help

CodePudding user response：

Or if you aren't allowed to change the ft variable, do:

>>> df[df[ft].squeeze() == 3]
   a  b
1  3  4
>>>

CodePudding user response：

Use scalar ft="a" for Series df['a'] instead one column DataFrame df[['a']] if ft=["a"].

If need test index use:

ft = 3
dt = df.loc[ft]

If not sure if exist:

ft = 3
dt = df[df.index == ft]

For first column use:

ft = 3
dt = df[df.iloc[:, 0] == ft]