python - Pandas - Dataframe.set_index - how to keep the old index column
Your DataFrame df
has name
(= 'Bertram', 'Donald', 'Hugo'
) as index
That is, your df
is:
age weight
name
Bertram 45 65
Donald 75 85
Hugo 21 75
You can convert the index (name
) into a new column inside your DataFrame df
by using the .reset_index()
method.
df.reset_index(inplace=True)
name
becomes a column and the new index is the standard default integer index:
Your df looks like this now:
Out[1]:
name age weight
0 Bertram 45 65
1 Donald 75 85
2 Hugo 21 75
Now, you can change the index to age
with the .set_index()
method.
df.set_index('age',inplace=True)
df
is now:
Out[2]:
name weight
age
45 Bertram 65
75 Donald 85
21 Hugo 75
As @jezrael points out above you can do this in a single step, instead of two steps, like this:
df = df.reset_index().set_index('age')
Use reset_index
first and then set_index
:
df = df.reset_index().set_index('age')
print (df)
name weight
age
45 Bertram 65
75 Donald 85
21 Hugo 75
Adding the append=True
and with reset_index
df.set_index('age', append=True).reset_index(level=0)
Out[80]:
name weight
age
45 Bertram 65
75 Donald 85
21 Hugo 75