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base.py
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"""
An interface for extending pandas with custom arrays.
.. warning::
This is an experimental API and subject to breaking changes
without warning.
"""
from __future__ import annotations
import operator
from typing import (
TYPE_CHECKING,
Any,
Callable,
ClassVar,
Iterator,
Literal,
Sequence,
TypeVar,
cast,
overload,
)
import numpy as np
from pandas._libs import (
groupby as libgroupby,
lib,
)
from pandas._typing import (
ArrayLike,
AstypeArg,
AxisInt,
Dtype,
FillnaOptions,
PositionalIndexer,
ScalarIndexer,
SequenceIndexer,
Shape,
SortKind,
TakeIndexer,
npt,
)
from pandas.compat import set_function_name
from pandas.compat.numpy import function as nv
from pandas.errors import AbstractMethodError
from pandas.util._decorators import (
Appender,
Substitution,
cache_readonly,
)
from pandas.util._validators import (
validate_bool_kwarg,
validate_fillna_kwargs,
validate_insert_loc,
)
from pandas.core.dtypes.cast import maybe_cast_to_extension_array
from pandas.core.dtypes.common import (
is_datetime64_dtype,
is_dtype_equal,
is_list_like,
is_object_dtype,
is_scalar,
is_timedelta64_dtype,
pandas_dtype,
)
from pandas.core.dtypes.dtypes import ExtensionDtype
from pandas.core.dtypes.generic import (
ABCDataFrame,
ABCIndex,
ABCSeries,
)
from pandas.core.dtypes.missing import isna
from pandas.core import (
arraylike,
missing,
roperator,
)
from pandas.core.algorithms import (
factorize_array,
isin,
mode,
rank,
unique,
)
from pandas.core.array_algos.quantile import quantile_with_mask
from pandas.core.sorting import (
nargminmax,
nargsort,
)
if TYPE_CHECKING:
from pandas._typing import (
NumpySorter,
NumpyValueArrayLike,
)
_extension_array_shared_docs: dict[str, str] = {}
ExtensionArrayT = TypeVar("ExtensionArrayT", bound="ExtensionArray")
class ExtensionArray:
"""
Abstract base class for custom 1-D array types.
pandas will recognize instances of this class as proper arrays
with a custom type and will not attempt to coerce them to objects. They
may be stored directly inside a :class:`DataFrame` or :class:`Series`.
Attributes
----------
dtype
nbytes
ndim
shape
Methods
-------
argsort
astype
copy
dropna
factorize
fillna
equals
insert
isin
isna
ravel
repeat
searchsorted
shift
take
tolist
unique
view
_accumulate
_concat_same_type
_formatter
_from_factorized
_from_sequence
_from_sequence_of_strings
_reduce
_values_for_argsort
_values_for_factorize
Notes
-----
The interface includes the following abstract methods that must be
implemented by subclasses:
* _from_sequence
* _from_factorized
* __getitem__
* __len__
* __eq__
* dtype
* nbytes
* isna
* take
* copy
* _concat_same_type
A default repr displaying the type, (truncated) data, length,
and dtype is provided. It can be customized or replaced by
by overriding:
* __repr__ : A default repr for the ExtensionArray.
* _formatter : Print scalars inside a Series or DataFrame.
Some methods require casting the ExtensionArray to an ndarray of Python
objects with ``self.astype(object)``, which may be expensive. When
performance is a concern, we highly recommend overriding the following
methods:
* fillna
* dropna
* unique
* factorize / _values_for_factorize
* argsort, argmax, argmin / _values_for_argsort
* searchsorted
The remaining methods implemented on this class should be performant,
as they only compose abstract methods. Still, a more efficient
implementation may be available, and these methods can be overridden.
One can implement methods to handle array accumulations or reductions.
* _accumulate
* _reduce
One can implement methods to handle parsing from strings that will be used
in methods such as ``pandas.io.parsers.read_csv``.
* _from_sequence_of_strings
This class does not inherit from 'abc.ABCMeta' for performance reasons.
Methods and properties required by the interface raise
``pandas.errors.AbstractMethodError`` and no ``register`` method is
provided for registering virtual subclasses.
ExtensionArrays are limited to 1 dimension.
They may be backed by none, one, or many NumPy arrays. For example,
``pandas.Categorical`` is an extension array backed by two arrays,
one for codes and one for categories. An array of IPv6 address may
be backed by a NumPy structured array with two fields, one for the
lower 64 bits and one for the upper 64 bits. Or they may be backed
by some other storage type, like Python lists. Pandas makes no
assumptions on how the data are stored, just that it can be converted
to a NumPy array.
The ExtensionArray interface does not impose any rules on how this data
is stored. However, currently, the backing data cannot be stored in
attributes called ``.values`` or ``._values`` to ensure full compatibility
with pandas internals. But other names as ``.data``, ``._data``,
``._items``, ... can be freely used.
If implementing NumPy's ``__array_ufunc__`` interface, pandas expects
that
1. You defer by returning ``NotImplemented`` when any Series are present
in `inputs`. Pandas will extract the arrays and call the ufunc again.
2. You define a ``_HANDLED_TYPES`` tuple as an attribute on the class.
Pandas inspect this to determine whether the ufunc is valid for the
types present.
See :ref:`extending.extension.ufunc` for more.
By default, ExtensionArrays are not hashable. Immutable subclasses may
override this behavior.
"""
# '_typ' is for pandas.core.dtypes.generic.ABCExtensionArray.
# Don't override this.
_typ = "extension"
# ------------------------------------------------------------------------
# Constructors
# ------------------------------------------------------------------------
@classmethod
def _from_sequence(cls, scalars, *, dtype: Dtype | None = None, copy: bool = False):
"""
Construct a new ExtensionArray from a sequence of scalars.
Parameters
----------
scalars : Sequence
Each element will be an instance of the scalar type for this
array, ``cls.dtype.type`` or be converted into this type in this method.
dtype : dtype, optional
Construct for this particular dtype. This should be a Dtype
compatible with the ExtensionArray.
copy : bool, default False
If True, copy the underlying data.
Returns
-------
ExtensionArray
"""
raise AbstractMethodError(cls)
@classmethod
def _from_sequence_of_strings(
cls, strings, *, dtype: Dtype | None = None, copy: bool = False
):
"""
Construct a new ExtensionArray from a sequence of strings.
Parameters
----------
strings : Sequence
Each element will be an instance of the scalar type for this
array, ``cls.dtype.type``.
dtype : dtype, optional
Construct for this particular dtype. This should be a Dtype
compatible with the ExtensionArray.
copy : bool, default False
If True, copy the underlying data.
Returns
-------
ExtensionArray
"""
raise AbstractMethodError(cls)
@classmethod
def _from_factorized(cls, values, original):
"""
Reconstruct an ExtensionArray after factorization.
Parameters
----------
values : ndarray
An integer ndarray with the factorized values.
original : ExtensionArray
The original ExtensionArray that factorize was called on.
See Also
--------
factorize : Top-level factorize method that dispatches here.
ExtensionArray.factorize : Encode the extension array as an enumerated type.
"""
raise AbstractMethodError(cls)
# ------------------------------------------------------------------------
# Must be a Sequence
# ------------------------------------------------------------------------
@overload
def __getitem__(self, item: ScalarIndexer) -> Any:
...
@overload
def __getitem__(self: ExtensionArrayT, item: SequenceIndexer) -> ExtensionArrayT:
...
def __getitem__(
self: ExtensionArrayT, item: PositionalIndexer
) -> ExtensionArrayT | Any:
"""
Select a subset of self.
Parameters
----------
item : int, slice, or ndarray
* int: The position in 'self' to get.
* slice: A slice object, where 'start', 'stop', and 'step' are
integers or None
* ndarray: A 1-d boolean NumPy ndarray the same length as 'self'
* list[int]: A list of int
Returns
-------
item : scalar or ExtensionArray
Notes
-----
For scalar ``item``, return a scalar value suitable for the array's
type. This should be an instance of ``self.dtype.type``.
For slice ``key``, return an instance of ``ExtensionArray``, even
if the slice is length 0 or 1.
For a boolean mask, return an instance of ``ExtensionArray``, filtered
to the values where ``item`` is True.
"""
raise AbstractMethodError(self)
def __setitem__(self, key, value) -> None:
"""
Set one or more values inplace.
This method is not required to satisfy the pandas extension array
interface.
Parameters
----------
key : int, ndarray, or slice
When called from, e.g. ``Series.__setitem__``, ``key`` will be
one of
* scalar int
* ndarray of integers.
* boolean ndarray
* slice object
value : ExtensionDtype.type, Sequence[ExtensionDtype.type], or object
value or values to be set of ``key``.
Returns
-------
None
"""
# Some notes to the ExtensionArray implementor who may have ended up
# here. While this method is not required for the interface, if you
# *do* choose to implement __setitem__, then some semantics should be
# observed:
#
# * Setting multiple values : ExtensionArrays should support setting
# multiple values at once, 'key' will be a sequence of integers and
# 'value' will be a same-length sequence.
#
# * Broadcasting : For a sequence 'key' and a scalar 'value',
# each position in 'key' should be set to 'value'.
#
# * Coercion : Most users will expect basic coercion to work. For
# example, a string like '2018-01-01' is coerced to a datetime
# when setting on a datetime64ns array. In general, if the
# __init__ method coerces that value, then so should __setitem__
# Note, also, that Series/DataFrame.where internally use __setitem__
# on a copy of the data.
raise NotImplementedError(f"{type(self)} does not implement __setitem__.")
def __len__(self) -> int:
"""
Length of this array
Returns
-------
length : int
"""
raise AbstractMethodError(self)
def __iter__(self) -> Iterator[Any]:
"""
Iterate over elements of the array.
"""
# This needs to be implemented so that pandas recognizes extension
# arrays as list-like. The default implementation makes successive
# calls to ``__getitem__``, which may be slower than necessary.
for i in range(len(self)):
yield self[i]
def __contains__(self, item: object) -> bool | np.bool_:
"""
Return for `item in self`.
"""
# GH37867
# comparisons of any item to pd.NA always return pd.NA, so e.g. "a" in [pd.NA]
# would raise a TypeError. The implementation below works around that.
if is_scalar(item) and isna(item):
if not self._can_hold_na:
return False
elif item is self.dtype.na_value or isinstance(item, self.dtype.type):
return self._hasna
else:
return False
else:
# error: Item "ExtensionArray" of "Union[ExtensionArray, ndarray]" has no
# attribute "any"
return (item == self).any() # type: ignore[union-attr]
# error: Signature of "__eq__" incompatible with supertype "object"
def __eq__(self, other: Any) -> ArrayLike: # type: ignore[override]
"""
Return for `self == other` (element-wise equality).
"""
# Implementer note: this should return a boolean numpy ndarray or
# a boolean ExtensionArray.
# When `other` is one of Series, Index, or DataFrame, this method should
# return NotImplemented (to ensure that those objects are responsible for
# first unpacking the arrays, and then dispatch the operation to the
# underlying arrays)
raise AbstractMethodError(self)
# error: Signature of "__ne__" incompatible with supertype "object"
def __ne__(self, other: Any) -> ArrayLike: # type: ignore[override]
"""
Return for `self != other` (element-wise in-equality).
"""
return ~(self == other)
def to_numpy(
self,
dtype: npt.DTypeLike | None = None,
copy: bool = False,
na_value: object = lib.no_default,
) -> np.ndarray:
"""
Convert to a NumPy ndarray.
.. versionadded:: 1.0.0
This is similar to :meth:`numpy.asarray`, but may provide additional control
over how the conversion is done.
Parameters
----------
dtype : str or numpy.dtype, optional
The dtype to pass to :meth:`numpy.asarray`.
copy : bool, default False
Whether to ensure that the returned value is a not a view on
another array. Note that ``copy=False`` does not *ensure* that
``to_numpy()`` is no-copy. Rather, ``copy=True`` ensure that
a copy is made, even if not strictly necessary.
na_value : Any, optional
The value to use for missing values. The default value depends
on `dtype` and the type of the array.
Returns
-------
numpy.ndarray
"""
result = np.asarray(self, dtype=dtype)
if copy or na_value is not lib.no_default:
result = result.copy()
if na_value is not lib.no_default:
result[self.isna()] = na_value
return result
# ------------------------------------------------------------------------
# Required attributes
# ------------------------------------------------------------------------
@property
def dtype(self) -> ExtensionDtype:
"""
An instance of 'ExtensionDtype'.
"""
raise AbstractMethodError(self)
@property
def shape(self) -> Shape:
"""
Return a tuple of the array dimensions.
"""
return (len(self),)
@property
def size(self) -> int:
"""
The number of elements in the array.
"""
# error: Incompatible return value type (got "signedinteger[_64Bit]",
# expected "int") [return-value]
return np.prod(self.shape) # type: ignore[return-value]
@property
def ndim(self) -> int:
"""
Extension Arrays are only allowed to be 1-dimensional.
"""
return 1
@property
def nbytes(self) -> int:
"""
The number of bytes needed to store this object in memory.
"""
# If this is expensive to compute, return an approximate lower bound
# on the number of bytes needed.
raise AbstractMethodError(self)
# ------------------------------------------------------------------------
# Additional Methods
# ------------------------------------------------------------------------
@overload
def astype(self, dtype: npt.DTypeLike, copy: bool = ...) -> np.ndarray:
...
@overload
def astype(self, dtype: ExtensionDtype, copy: bool = ...) -> ExtensionArray:
...
@overload
def astype(self, dtype: AstypeArg, copy: bool = ...) -> ArrayLike:
...
def astype(self, dtype: AstypeArg, copy: bool = True) -> ArrayLike:
"""
Cast to a NumPy array or ExtensionArray with 'dtype'.
Parameters
----------
dtype : str or dtype
Typecode or data-type to which the array is cast.
copy : bool, default True
Whether to copy the data, even if not necessary. If False,
a copy is made only if the old dtype does not match the
new dtype.
Returns
-------
np.ndarray or pandas.api.extensions.ExtensionArray
An ExtensionArray if dtype is ExtensionDtype,
Otherwise a NumPy ndarray with 'dtype' for its dtype.
"""
dtype = pandas_dtype(dtype)
if is_dtype_equal(dtype, self.dtype):
if not copy:
return self
else:
return self.copy()
if isinstance(dtype, ExtensionDtype):
cls = dtype.construct_array_type()
return cls._from_sequence(self, dtype=dtype, copy=copy)
elif is_datetime64_dtype(dtype):
from pandas.core.arrays import DatetimeArray
return DatetimeArray._from_sequence(self, dtype=dtype, copy=copy)
elif is_timedelta64_dtype(dtype):
from pandas.core.arrays import TimedeltaArray
return TimedeltaArray._from_sequence(self, dtype=dtype, copy=copy)
return np.array(self, dtype=dtype, copy=copy)
def isna(self) -> np.ndarray | ExtensionArraySupportsAnyAll:
"""
A 1-D array indicating if each value is missing.
Returns
-------
numpy.ndarray or pandas.api.extensions.ExtensionArray
In most cases, this should return a NumPy ndarray. For
exceptional cases like ``SparseArray``, where returning
an ndarray would be expensive, an ExtensionArray may be
returned.
Notes
-----
If returning an ExtensionArray, then
* ``na_values._is_boolean`` should be True
* `na_values` should implement :func:`ExtensionArray._reduce`
* ``na_values.any`` and ``na_values.all`` should be implemented
"""
raise AbstractMethodError(self)
@property
def _hasna(self) -> bool:
# GH#22680
"""
Equivalent to `self.isna().any()`.
Some ExtensionArray subclasses may be able to optimize this check.
"""
return bool(self.isna().any())
def _values_for_argsort(self) -> np.ndarray:
"""
Return values for sorting.
Returns
-------
ndarray
The transformed values should maintain the ordering between values
within the array.
See Also
--------
ExtensionArray.argsort : Return the indices that would sort this array.
Notes
-----
The caller is responsible for *not* modifying these values in-place, so
it is safe for implementors to give views on `self`.
Functions that use this (e.g. ExtensionArray.argsort) should ignore
entries with missing values in the original array (according to `self.isna()`).
This means that the corresponding entries in the returned array don't need to
be modified to sort correctly.
"""
# Note: this is used in `ExtensionArray.argsort/argmin/argmax`.
return np.array(self)
def argsort(
self,
*,
ascending: bool = True,
kind: SortKind = "quicksort",
na_position: str = "last",
**kwargs,
) -> np.ndarray:
"""
Return the indices that would sort this array.
Parameters
----------
ascending : bool, default True
Whether the indices should result in an ascending
or descending sort.
kind : {'quicksort', 'mergesort', 'heapsort', 'stable'}, optional
Sorting algorithm.
*args, **kwargs:
Passed through to :func:`numpy.argsort`.
Returns
-------
np.ndarray[np.intp]
Array of indices that sort ``self``. If NaN values are contained,
NaN values are placed at the end.
See Also
--------
numpy.argsort : Sorting implementation used internally.
"""
# Implementor note: You have two places to override the behavior of
# argsort.
# 1. _values_for_argsort : construct the values passed to np.argsort
# 2. argsort : total control over sorting. In case of overriding this,
# it is recommended to also override argmax/argmin
ascending = nv.validate_argsort_with_ascending(ascending, (), kwargs)
values = self._values_for_argsort()
return nargsort(
values,
kind=kind,
ascending=ascending,
na_position=na_position,
mask=np.asarray(self.isna()),
)
def argmin(self, skipna: bool = True) -> int:
"""
Return the index of minimum value.
In case of multiple occurrences of the minimum value, the index
corresponding to the first occurrence is returned.
Parameters
----------
skipna : bool, default True
Returns
-------
int
See Also
--------
ExtensionArray.argmax
"""
# Implementor note: You have two places to override the behavior of
# argmin.
# 1. _values_for_argsort : construct the values used in nargminmax
# 2. argmin itself : total control over sorting.
validate_bool_kwarg(skipna, "skipna")
if not skipna and self._hasna:
raise NotImplementedError
return nargminmax(self, "argmin")
def argmax(self, skipna: bool = True) -> int:
"""
Return the index of maximum value.
In case of multiple occurrences of the maximum value, the index
corresponding to the first occurrence is returned.
Parameters
----------
skipna : bool, default True
Returns
-------
int
See Also
--------
ExtensionArray.argmin
"""
# Implementor note: You have two places to override the behavior of
# argmax.
# 1. _values_for_argsort : construct the values used in nargminmax
# 2. argmax itself : total control over sorting.
validate_bool_kwarg(skipna, "skipna")
if not skipna and self._hasna:
raise NotImplementedError
return nargminmax(self, "argmax")
def fillna(
self: ExtensionArrayT,
value: object | ArrayLike | None = None,
method: FillnaOptions | None = None,
limit: int | None = None,
) -> ExtensionArrayT:
"""
Fill NA/NaN values using the specified method.
Parameters
----------
value : scalar, array-like
If a scalar value is passed it is used to fill all missing values.
Alternatively, an array-like 'value' can be given. It's expected
that the array-like have the same length as 'self'.
method : {'backfill', 'bfill', 'pad', 'ffill', None}, default None
Method to use for filling holes in reindexed Series:
* pad / ffill: propagate last valid observation forward to next valid.
* backfill / bfill: use NEXT valid observation to fill gap.
limit : int, default None
If method is specified, this is the maximum number of consecutive
NaN values to forward/backward fill. In other words, if there is
a gap with more than this number of consecutive NaNs, it will only
be partially filled. If method is not specified, this is the
maximum number of entries along the entire axis where NaNs will be
filled.
Returns
-------
ExtensionArray
With NA/NaN filled.
"""
value, method = validate_fillna_kwargs(value, method)
mask = self.isna()
# error: Argument 2 to "check_value_size" has incompatible type
# "ExtensionArray"; expected "ndarray"
value = missing.check_value_size(
value, mask, len(self) # type: ignore[arg-type]
)
if mask.any():
if method is not None:
func = missing.get_fill_func(method)
npvalues = self.astype(object)
func(npvalues, limit=limit, mask=mask)
new_values = self._from_sequence(npvalues, dtype=self.dtype)
else:
# fill with value
new_values = self.copy()
new_values[mask] = value
else:
new_values = self.copy()
return new_values
def dropna(self: ExtensionArrayT) -> ExtensionArrayT:
"""
Return ExtensionArray without NA values.
Returns
-------
pandas.api.extensions.ExtensionArray
"""
# error: Unsupported operand type for ~ ("ExtensionArray")
return self[~self.isna()] # type: ignore[operator]
def shift(self, periods: int = 1, fill_value: object = None) -> ExtensionArray:
"""
Shift values by desired number.
Newly introduced missing values are filled with
``self.dtype.na_value``.
Parameters
----------
periods : int, default 1
The number of periods to shift. Negative values are allowed
for shifting backwards.
fill_value : object, optional
The scalar value to use for newly introduced missing values.
The default is ``self.dtype.na_value``.
Returns
-------
ExtensionArray
Shifted.
Notes
-----
If ``self`` is empty or ``periods`` is 0, a copy of ``self`` is
returned.
If ``periods > len(self)``, then an array of size
len(self) is returned, with all values filled with
``self.dtype.na_value``.
"""
# Note: this implementation assumes that `self.dtype.na_value` can be
# stored in an instance of your ExtensionArray with `self.dtype`.
if not len(self) or periods == 0:
return self.copy()
if isna(fill_value):
fill_value = self.dtype.na_value
empty = self._from_sequence(
[fill_value] * min(abs(periods), len(self)), dtype=self.dtype
)
if periods > 0:
a = empty
b = self[:-periods]
else:
a = self[abs(periods) :]
b = empty
return self._concat_same_type([a, b])
def unique(self: ExtensionArrayT) -> ExtensionArrayT:
"""
Compute the ExtensionArray of unique values.
Returns
-------
pandas.api.extensions.ExtensionArray
"""
uniques = unique(self.astype(object))
return self._from_sequence(uniques, dtype=self.dtype)
def searchsorted(
self,
value: NumpyValueArrayLike | ExtensionArray,
side: Literal["left", "right"] = "left",
sorter: NumpySorter = None,
) -> npt.NDArray[np.intp] | np.intp:
"""
Find indices where elements should be inserted to maintain order.
Find the indices into a sorted array `self` (a) such that, if the
corresponding elements in `value` were inserted before the indices,
the order of `self` would be preserved.
Assuming that `self` is sorted:
====== ================================
`side` returned index `i` satisfies
====== ================================
left ``self[i-1] < value <= self[i]``
right ``self[i-1] <= value < self[i]``
====== ================================
Parameters
----------
value : array-like, list or scalar
Value(s) to insert into `self`.
side : {'left', 'right'}, optional
If 'left', the index of the first suitable location found is given.
If 'right', return the last such index. If there is no suitable
index, return either 0 or N (where N is the length of `self`).
sorter : 1-D array-like, optional
Optional array of integer indices that sort array a into ascending
order. They are typically the result of argsort.
Returns
-------
array of ints or int
If value is array-like, array of insertion points.
If value is scalar, a single integer.
See Also
--------
numpy.searchsorted : Similar method from NumPy.
"""
# Note: the base tests provided by pandas only test the basics.
# We do not test
# 1. Values outside the range of the `data_for_sorting` fixture
# 2. Values between the values in the `data_for_sorting` fixture
# 3. Missing values.
arr = self.astype(object)
if isinstance(value, ExtensionArray):
value = value.astype(object)
return arr.searchsorted(value, side=side, sorter=sorter)
def equals(self, other: object) -> bool:
"""
Return if another array is equivalent to this array.
Equivalent means that both arrays have the same shape and dtype, and
all values compare equal. Missing values in the same location are
considered equal (in contrast with normal equality).
Parameters
----------
other : ExtensionArray
Array to compare to this Array.
Returns
-------
boolean
Whether the arrays are equivalent.
"""
if type(self) != type(other):
return False
other = cast(ExtensionArray, other)
if not is_dtype_equal(self.dtype, other.dtype):
return False
elif len(self) != len(other):
return False
else:
equal_values = self == other
if isinstance(equal_values, ExtensionArray):
# boolean array with NA -> fill with False
equal_values = equal_values.fillna(False)
# error: Unsupported left operand type for & ("ExtensionArray")
equal_na = self.isna() & other.isna() # type: ignore[operator]
return bool((equal_values | equal_na).all())
def isin(self, values) -> npt.NDArray[np.bool_]:
"""
Pointwise comparison for set containment in the given values.
Roughly equivalent to `np.array([x in values for x in self])`
Parameters
----------
values : Sequence
Returns
-------
np.ndarray[bool]
"""
return isin(np.asarray(self), values)
def _values_for_factorize(self) -> tuple[np.ndarray, Any]:
"""
Return an array and missing value suitable for factorization.
Returns