I want to slice a dataframe using a condition based on a DateTime column's month, element by element:
Met_Monthly_DF = Metsite_DF.iloc[Metsite_DF['DateTime'].month == Month]
I get the error:
builtins.AttributeError: 'Series' object has no attribute 'month'
It works on an element by element basis if I do say:
Months = [DT.month for DT in Metsite_DF['DateTime'].tolist()]
How do I apply this condition?
There are 2 problems:
dt - here dt.monthboolean indexing change iloc to locMet_Monthly_DF = Metsite_DF.loc[Metsite_DF['DateTime'].dt.month == Month]
Sample:
Metsite_DF = pd.DataFrame({'col':list('abcd'),
'DateTime':pd.date_range('2017-01-01', periods=4, freq='16D')})
print (Metsite_DF)
DateTime col
0 2017-01-01 a
1 2017-01-17 b
2 2017-02-02 c
3 2017-02-18 d
Month = 2
Met_Monthly_DF = Metsite_DF.loc[Metsite_DF['DateTime'].dt.month == Month]
print (Met_Monthly_DF)
DateTime col
2 2017-02-02 c
3 2017-02-18 d
Or remove iloc, but then obviously need copy for avoid SettingWithCopyWarning:
Met_Monthly_DF = Metsite_DF[Metsite_DF['DateTime'].dt.month == Month].copy()
If you modify values in Met_Monthly_DF later you will find that the modifications do not propagate back to the original data (Metsite_DF), and that Pandas does warning.
Month = 2
Met_Monthly_DF = Metsite_DF[Metsite_DF['DateTime'].dt.month == Month]
#filter dataframe is modified - e.g. added new column for years
Met_Monthly_DF['new'] = Met_Monthly_DF['DateTime'].dt.year
print (Met_Monthly_DF)
DateTime col new
2 2017-02-02 c 2017
3 2017-02-18 d 2017
SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame. Try using .loc[row_indexer,col_indexer] = value instead
See the caveats in the documentation: http://pandas.pydata.org/pandas-docs/stable/indexing.html#indexing-view-versus-copy
Month = 2
Met_Monthly_DF = Metsite_DF[Metsite_DF['DateTime'].dt.month == Month].copy()
Met_Monthly_DF['new'] = Met_Monthly_DF['DateTime'].dt.year
print (Met_Monthly_DF)
DateTime col new
2 2017-02-02 c 2017
3 2017-02-18 d 2017
