pandas.Series.rank

Series.rank(self, axis=0, method='average', numeric_only=None, na_option='keep', ascending=True, pct=False)[source]

Compute numerical data ranks (1 through n) along axis.

By default, equal values are assigned a rank that is the average of the ranks of those values.

Parameters
axis{0 or ‘index’, 1 or ‘columns’}, default 0

Index to direct ranking.

method{‘average’, ‘min’, ‘max’, ‘first’, ‘dense’}, default ‘average’

How to rank the group of records that have the same value (i.e. ties):

  • average: average rank of the group

  • min: lowest rank in the group

  • max: highest rank in the group

  • first: ranks assigned in order they appear in the array

  • dense: like ‘min’, but rank always increases by 1 between groups

numeric_onlybool, optional

For DataFrame objects, rank only numeric columns if set to True.

na_option{‘keep’, ‘top’, ‘bottom’}, default ‘keep’

How to rank NaN values:

  • keep: assign NaN rank to NaN values

  • top: assign smallest rank to NaN values if ascending

  • bottom: assign highest rank to NaN values if ascending

ascendingbool, default True

Whether or not the elements should be ranked in ascending order.

pctbool, default False

Whether or not to display the returned rankings in percentile form.

Returns
same type as caller

Return a Series or DataFrame with data ranks as values.

See also

core.groupby.GroupBy.rank

Rank of values within each group.

Examples

>>> df = pd.DataFrame(data={'Animal': ['cat', 'penguin', 'dog',
...                                    'spider', 'snake'],
...                         'Number_legs': [4, 2, 4, 8, np.nan]})
>>> df
    Animal  Number_legs
0      cat          4.0
1  penguin          2.0
2      dog          4.0
3   spider          8.0
4    snake          NaN

The following example shows how the method behaves with the above parameters:

  • default_rank: this is the default behaviour obtained without using any parameter.

  • max_rank: setting method = 'max' the records that have the same values are ranked using the highest rank (e.g.: since ‘cat’ and ‘dog’ are both in the 2nd and 3rd position, rank 3 is assigned.)

  • NA_bottom: choosing na_option = 'bottom', if there are records with NaN values they are placed at the bottom of the ranking.

  • pct_rank: when setting pct = True, the ranking is expressed as percentile rank.

>>> df['default_rank'] = df['Number_legs'].rank()
>>> df['max_rank'] = df['Number_legs'].rank(method='max')
>>> df['NA_bottom'] = df['Number_legs'].rank(na_option='bottom')
>>> df['pct_rank'] = df['Number_legs'].rank(pct=True)
>>> df
    Animal  Number_legs  default_rank  max_rank  NA_bottom  pct_rank
0      cat          4.0           2.5       3.0        2.5     0.625
1  penguin          2.0           1.0       1.0        1.0     0.250
2      dog          4.0           2.5       3.0        2.5     0.625
3   spider          8.0           4.0       4.0        4.0     1.000
4    snake          NaN           NaN       NaN        5.0       NaN
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