Polars Series

Code

import polars as pl

Create

Create a new Series

Create empty series

Action	Code	Details
Empty series (of object type)	pl.Series()
Empty boolean series	pl.Series(dtype=pl.Boolean)
Empty enum series	pl.Series(dtype=pl.Enum(['a', 'b', 'c']))
Empty categorical series without defined categories	pl.Series(dtype=pl.Categorical)
Empty int series	pl.Series(dtype=pl.Int64)
Empty float series	pl.Series(dtype=pl.Float64)
Empty date series	pl.Series(dtype=pl.Date)
Empty datetime series	pl.Series(dtype=pl.Datetime)
Empty list series	pl.Series(dtype=pl.List)
Empty list of floats series	pl.Series(dtype=pl.List(float))

Create series of constant values

Action	Code	Details
Series of length n filled with nulls	pl.Series([None] * n)
Constant value v of length n	pl.Series([v] * n)

Create List series

Action	Code	Details
Define list series with multiple list elements	pl.Series([[1], [2, 3], [])
Define scalar list series	pl.Series([[1, 2, 3]])
Create scalar list series from a list	x = [1, 2, 3] pl.Series([x])
Create list series from a list of lists	x = [ [1, 2], [], [3, 4, 5], [6] ] pl.Series(x)

Test

Action	Code	Details
Is series or subclass	isinstance(x, pl.Series)
Is series and not subclass	type(x) is pl.Series
Empty	x.is_empty()
Not empty	not x.is_empty()
Has length n	len(x) == n
Is boolean series	x.dtype == pl.Boolean
Is categorical series	x.dtype == pl.Categorical
Is enum series	x.dtype == pl.Enum
Is numeric series	x.dtype.is_numeric()	For example, pl.Int8 or pl.Float64
Is integer series	x.dtype.is_integer()
Is unsigned integer series	x.dtype.is_unsigned_integer()
Is float series	x.dtype.is_float()
Is date series	x.dtype == pl.Date
Is datetime64 series	x.dtype == pl.Datetime
Is string series	x.dtype == pl.String
Is list series	x.dtype == pl.List
Is nested series (struct or list)	x.dtype.is_nested()
No duplicate elements (all unique)	x.is_unique().all()
Any duplicate elements	x.is_duplicated().any()
Contains null	x.has_nulls()
Contains only nulls	x.is_null().all()
Contains no nulls	not x.has_nulls()
Contains NaN	x.is_nan().any()
Contains no NaNs	x.is_not_nan().all()
Contains infinity	x.is_infinite().any()
Contains only finite values	x.is_finite().all()
Contains value v, ignoring nulls	v in x
Contains any of the values v1, v2, ignoring nulls	x.is_in([v1, v2]).any()
Does not contain value v	v not in x
Are elements in increasing order	x.is_sorted()	Presence of nulls can lead to unexpected behavior, as they need to come first.
Are elements in decreasing order	x.is_sorted(descending=True)	Presence of nulls can lead to unexpected behavior, as they need to come first.

Test boolean series

Action	Code	Details
All values are True	x.all()
All values are False	not x.any()

Tests for string series

Action	Code	Details
Contains string s	x.str.contains(s).any()

Extract

Action	Code	Details
Number of elements	len(x)
Hash	hash(tuple(x))
Data type (dtype)	x.dtype
Number of unique elements, ignoring nulls	x.n_unique()
Smallest value, ignoring nulls	x.min()
Index of the smallest value, ignoring NAs	x.arg_min()
Greatest value, ignoring nulls	x.max()
Index of the greatest value, ignoring NAs	x.arg_max()
Count occurrence per value	x.value_counts()

Type-specific operations

Enum

Categorical

Action	Code	Details
Get categories	x.cat.get_categories()

String

List

Action	Code	Details
Get length of each list element	x.list.len()
Get the _i_th item of each list element	x.list[i]

Struct

Derive

Order

Action	Code	Details
Reverse	x.reverse()
Sort ascendingly	x.sort()	Nulls are placed first
Sort descendingly	x.sort(descending=True)	Nulls are placed first
Shuffle	x.shuffle()

Transform

Action	Code	Details
Fill null by value_v_	x.fill_null(value=v)
Fill NaN by value_v_	x.fill_nan(value=v)
Replace value v by w	x.replace(v, w)
Replace value v by null	x.replace(v, None)
Map all values	x = pl.Series([1, 2, 3]) x.replace_strict([1, 2, 3], [10, -2, -3])
Map all values using a dict	x = pl.Series([1, 2, 3]) x.replace_strict({1: 10, 2: -2, 3: -3})

Mask

Action	Code	Details
Duplicate mask	x.is_duplicated()

Cast to type

Action	Code	Details
Cast to boolean	x.cast(bool)
Cast series to numeric dtype	x.cast(float)
Cast to integer	x.cast(int)
Cast to float	x.cast(float)
Cast to string	x.cast(str)
Cast to categorical	x.cast(str).cast(pl.Categorical)
Cast categorical to integer codes	x.to_physical()
Cast to enum	x.cast(pl.Enum)
Cast enum to integer codes	x.to_physical()

Grow

Shrink

Action	Code	Details
First n elements	x.head(n)
Last n elements	x.tail(n)
Slice	x[a:b]
Select n elements starting from index i	x.slice(i, n)
Keep indices	x.gather([1, 3])
Keep every n_th element, starting from index _i	x.gather_every(n, i)
Sample n elements	x.sample(n)
Drop null elements	x.drop_nulls()
Drop NaN elements	x.drop_nans()
Keep n largest elements	x.top_k(n)
Keep n smallest elements	x.bottom_k(n)
Remove duplicates	x.unique()

Combine

Action	Code	Details
Append another series	x.append(y)

Convert

Action	Code	Details
To list	x.to_list()
To list	list(x)
To numpy array	x.to_numpy()
To Polars data frame with single column	x.to_frame('col1')
To instantiatable string representation	x.to_init_repr()
Dummy encoding of values (as data frame)	x.to_dummies()