pandas Series.index behaviour not allowing to reassign index in a single-line operation

Question

In pandas I am calculating means of columns and I want to rename the columns appending the string _avg.

Following the example in the answer here works: so if I do:

ss = df[col_list].mean()
ss.index = [el+"_avg" for el in col_list]

But although df[col_list].mean() is a pandas.Series type doing:

ss = df[col_list].mean().index = [el+"_avg" for el in col_list]

returns a list of strings and

ss = pandas.Series(df[col_list].mean().index = [el+"_avg" for el in col_list])

is not working at all while as in the previous link

ss = pandas.Series(df[col_list].mean(), index= [el+"_avg" for el in col_list])

changes the names but the values become NaN. (This behaviour is actually explained in the doc)

Why is that and how can I merge the two expressions a single line?

`x = y.index = z` does `x = z` and then `y.index = x`. It doesn't do `x = y` and then `y.index = z`. — TigerhawkT3, Jan 23 '19 at 17:48
C.f. https://stackoverflow.com/questions/7601823/how-do-chained-assignments-work and https://stackoverflow.com/questions/11498441/what-is-this-kind-of-assignment-in-python-called-a-b-true. — TigerhawkT3, Jan 23 '19 at 17:50
Nope. Assignment chaining is kinda funny. Using multiple lines for multiple simple assignments is generally clearer and easier to read for this reason. — TigerhawkT3, Jan 23 '19 at 18:02

unutbu · Answer 1 · 2019-01-23T18:07:54.623

2

ss = df[col_list].mean().add_suffix('_avg')

For example,

In [75]: ss = pd.Series([1,2,3], list('ABC'))

In [76]: ss.add_suffix('_avg')
Out[76]: 
A_avg    1
B_avg    2
C_avg    3
dtype: int64

In [77]: ss.add_prefix('col_')
Out[77]: 
col_A    1
col_B    2
col_C    3
dtype: int64

edited Jan 23 '19 at 18:07

answered Jan 23 '19 at 17:56

unutbu

score 0 · Answer 2 · answered Jan 23 '19 at 17:48

0

Have you tried to extract the values from the series?

ss = pandas.Series(df[col_list].mean().values, index= [el+"_avg" for el in col_list])

answered Jan 23 '19 at 17:48

nick

2 Answers2