CODEWITHSUNDEEP
pythonsortingpandasdataframe
Jason Yang
Jason Yang

Reputation: 584

How to sort a Series or DataFrame by a given index order?

Suppose I have a Series like this:

In [19]: sr
Out[19]: 
a    1
b    2
c    3
d    4
dtype: int64

In [20]: sr.index
Out[20]: Index([u'a', u'b', u'c', u'd'], dtype='object')

Instead of sorting lexicographically, I would like to sort this series based on a custom order, say, cdab. How can I do that?

What if it is a DataFrame; how can I sort it by a given index list?

Upvotes: 5

Views: 5430

Answers (2)

Alex Riley
Alex Riley

Reputation: 176938

You can do this in number of different ways. For Series objects, you can simply pass your preferred order for the index like this:

>>> sr[['c','d','a','b']]
c    3
d    4
a    1
b    2
dtype: int64

Alternatively, both Series and DataFrame objects have a reindex method. This allows you more flexibility when sorting the index. For instance, you can insert new values into the index (and even choose what value it should have):

>>> sr.reindex(['c','d','a','b','e'])
c     3
d     4
a     1
b     2
e   NaN      # <-- new index location 'e' is filled with NaN
dtype: int64

Yet another option for both Series and DataFrame objects is the ever-useful loc method of accessing index labels:

>>> sr.loc[['c','d','a','b']]
c    3
d    4
a    1
b    2
dtype: int64

Upvotes: 8

Matti John
Matti John

Reputation: 20507

Just use reindex, for example:

In [3]: sr.reindex(['c', 'd', 'a', 'b'])
Out[3]: 
c    3
d    4
a    1
b    2
dtype: int64

Upvotes: 2

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