accessor.py

"""Sparse accessor"""

from __future__ import annotations

from typing import TYPE_CHECKING

import numpy as np

from pandas.compat._optional import import_optional_dependency

from pandas.core.dtypes.cast import find_common_type
from pandas.core.dtypes.dtypes import SparseDtype

from pandas.core.accessor import (
    PandasDelegate,
    delegate_names,
)
from pandas.core.arrays.sparse.array import SparseArray

if TYPE_CHECKING:
    from scipy.sparse import (
        coo_matrix,
        spmatrix,
    )

    from pandas import (
        DataFrame,
        Series,
    )


class BaseAccessor:
    _validation_msg = "Can only use the '.sparse' accessor with Sparse data."

    def __init__(self, data=None) -> None:
        self._parent = data
        self._validate(data)

    def _validate(self, data) -> None:
        raise NotImplementedError


@delegate_names(
    SparseArray, ["npoints", "density", "fill_value", "sp_values"], typ="property"
)
class SparseAccessor(BaseAccessor, PandasDelegate):
    """
    Accessor for SparseSparse from other sparse matrix data types.

    Parameters
    ----------
    data : Series or DataFrame
        The Series or DataFrame to which the SparseAccessor is attached.

    See Also
    --------
    Series.sparse.to_coo : Create a scipy.sparse.coo_matrix from a Series with
        MultiIndex.
    Series.sparse.from_coo : Create a Series with sparse values from a
        scipy.sparse.coo_matrix.

    Examples
    --------
    >>> ser = pd.Series([0, 0, 2, 2, 2], dtype="Sparse[int]")
    >>> ser.sparse.density
    0.6
    >>> ser.sparse.sp_values
    array([2, 2, 2])
    """

    def _validate(self, data) -> None:
        if not isinstance(data.dtype, SparseDtype):
            raise AttributeError(self._validation_msg)

    def _delegate_property_get(self, name: str, *args, **kwargs):
        return getattr(self._parent.array, name)

    def _delegate_method(self, name: str, *args, **kwargs):
        if name == "from_coo":
            return self.from_coo(*args, **kwargs)
        elif name == "to_coo":
            return self.to_coo(*args, **kwargs)
        else:
            raise ValueError

    @classmethod
    def from_coo(cls, A, dense_index: bool = False) -> Series:
        """
        Create a Series with sparse values from a scipy.sparse.coo_matrix.

        This method takes a ``scipy.sparse.coo_matrix`` (coordinate format) as input and
        returns a pandas ``Series`` where the non-zero elements are represented as
        sparse values. The index of the Series can either include only the coordinates
        of non-zero elements (default behavior) or the full sorted set of coordinates
        from the matrix if ``dense_index`` is set to `True`.

        Parameters
        ----------
        A : scipy.sparse.coo_matrix
            The sparse matrix in coordinate format from which the sparse Series
            will be created.
        dense_index : bool, default False
            If False (default), the index consists of only the
            coords of the non-null entries of the original coo_matrix.
            If True, the index consists of the full sorted
            (row, col) coordinates of the coo_matrix.

        Returns
        -------
        s : Series
            A Series with sparse values.

        See Also
        --------
        DataFrame.sparse.from_spmatrix : Create a new DataFrame from a scipy sparse
            matrix.
        scipy.sparse.coo_matrix : A sparse matrix in COOrdinate format.

        Examples
        --------
        >>> from scipy import sparse

        >>> A = sparse.coo_matrix(
        ...     ([3.0, 1.0, 2.0], ([1, 0, 0], [0, 2, 3])), shape=(3, 4)
        ... )
        >>> A
        <COOrdinate sparse matrix of dtype 'float64'
            with 3 stored elements and shape (3, 4)>

        >>> A.todense()
        matrix([[0., 0., 1., 2.],
        [3., 0., 0., 0.],
        [0., 0., 0., 0.]])

        >>> ss = pd.Series.sparse.from_coo(A)
        >>> ss
        0  2    1.0
           3    2.0
        1  0    3.0
        dtype: Sparse[float64, nan]
        """
        from pandas import Series
        from pandas.core.arrays.sparse.scipy_sparse import coo_to_sparse_series

        result = coo_to_sparse_series(A, dense_index=dense_index)
        result = Series(result.array, index=result.index, copy=False)

        return result

    def to_coo(
        self, row_levels=(0,), column_levels=(1,), sort_labels: bool = False
    ) -> tuple[coo_matrix, list, list]:
        """
        Create a scipy.sparse.coo_matrix from a Series with MultiIndex.

        Use row_levels and column_levels to determine the row and column
        coordinates respectively. row_levels and column_levels are the names
        (labels) or numbers of the levels. {row_levels, column_levels} must be
        a partition of the MultiIndex level names (or numbers).

        Parameters
        ----------
        row_levels : tuple/list
            MultiIndex levels to use for row coordinates, specified by name or index.
        column_levels : tuple/list
            MultiIndex levels to use for column coordinates, specified by name or index.
        sort_labels : bool, default False
            Sort the row and column labels before forming the sparse matrix.
            When `row_levels` and/or `column_levels` refer to a single level,
            set to `True` for a faster execution.

        Returns
        -------
        y : scipy.sparse.coo_matrix
            The sparse matrix in coordinate format.
        rows : list (row labels)
            Labels corresponding to the row coordinates.
        columns : list (column labels)
            Labels corresponding to the column coordinates.

        See Also
        --------
        Series.sparse.from_coo : Create a Series with sparse values from a
            scipy.sparse.coo_matrix.

        Examples
        --------
        >>> s = pd.Series([3.0, np.nan, 1.0, 3.0, np.nan, np.nan])
        >>> s.index = pd.MultiIndex.from_tuples(
        ...     [
        ...         (1, 2, "a", 0),
        ...         (1, 2, "a", 1),
        ...         (1, 1, "b", 0),
        ...         (1, 1, "b", 1),
        ...         (2, 1, "b", 0),
        ...         (2, 1, "b", 1),
        ...     ],
        ...     names=["A", "B", "C", "D"],
        ... )
        >>> s
        A  B  C  D
        1  2  a  0    3.0
                 1    NaN
           1  b  0    1.0
                 1    3.0
        2  1  b  0    NaN
                 1    NaN
        dtype: float64

        >>> ss = s.astype("Sparse")
        >>> ss
        A  B  C  D
        1  2  a  0    3.0
                 1    NaN
           1  b  0    1.0
                 1    3.0
        2  1  b  0    NaN
                 1    NaN
        dtype: Sparse[float64, nan]

        >>> A, rows, columns = ss.sparse.to_coo(
        ...     row_levels=["A", "B"], column_levels=["C", "D"], sort_labels=True
        ... )
        >>> A
        <COOrdinate sparse matrix of dtype 'float64'
            with 3 stored elements and shape (3, 4)>
        >>> A.todense()
        matrix([[0., 0., 1., 3.],
        [3., 0., 0., 0.],
        [0., 0., 0., 0.]])

        >>> rows
        [(1, 1), (1, 2), (2, 1)]
        >>> columns
        [('a', 0), ('a', 1), ('b', 0), ('b', 1)]
        """
        from pandas.core.arrays.sparse.scipy_sparse import sparse_series_to_coo

        A, rows, columns = sparse_series_to_coo(
            self._parent, row_levels, column_levels, sort_labels=sort_labels
        )
        return A, rows, columns

    def to_dense(self) -> Series:
        """
        Convert a Series from sparse values to dense.

        Returns
        -------
        Series:
            A Series with the same values, stored as a dense array.

        Examples
        --------
        >>> series = pd.Series(pd.arrays.SparseArray([0, 1, 0]))
        >>> series
        0    0
        1    1
        2    0
        dtype: Sparse[int64, 0]

        >>> series.sparse.to_dense()
        0    0
        1    1
        2    0
        dtype: int64
        """
        from pandas import Series

        return Series(
            self._parent.array.to_dense(),
            index=self._parent.index,
            name=self._parent.name,
            copy=False,
        )


class SparseFrameAccessor(BaseAccessor, PandasDelegate):
    """
    DataFrame accessor for sparse data.

    It allows users to interact with a `DataFrame` that contains sparse data types
    (`SparseDtype`). It provides methods and attributes to efficiently work with sparse
    storage, reducing memory usage while maintaining compatibility with standard pandas
    operations.

    Parameters
    ----------
    data : scipy.sparse.spmatrix
        Must be convertible to csc format.

    See Also
    --------
    DataFrame.sparse.density : Ratio of non-sparse points to total (dense) data points.

    Examples
    --------
    >>> df = pd.DataFrame({"a": [1, 2, 0, 0], "b": [3, 0, 0, 4]}, dtype="Sparse[int]")
    >>> df.sparse.density
    np.float64(0.5)
    """

    def _validate(self, data) -> None:
        dtypes = data.dtypes
        if not all(isinstance(t, SparseDtype) for t in dtypes):
            raise AttributeError(self._validation_msg)

    @classmethod
    def from_spmatrix(cls, data, index=None, columns=None) -> DataFrame:
        """
        Create a new DataFrame from a scipy sparse matrix.

        Parameters
        ----------
        data : scipy.sparse.spmatrix
            Must be convertible to csc format.
        index, columns : Index, optional
            Row and column labels to use for the resulting DataFrame.
            Defaults to a RangeIndex.

        Returns
        -------
        DataFrame
            Each column of the DataFrame is stored as a
            :class:`arrays.SparseArray`.

        See Also
        --------
        DataFrame.sparse.to_coo : Return the contents of the frame as a
            sparse SciPy COO matrix.

        Examples
        --------
        >>> import scipy.sparse
        >>> mat = scipy.sparse.eye(3, dtype=int)
        >>> pd.DataFrame.sparse.from_spmatrix(mat)
             0    1    2
        0    1    0    0
        1    0    1    0
        2    0    0    1
        """
        from pandas._libs.sparse import IntIndex

        from pandas import DataFrame

        data = data.tocsc()
        index, columns = cls._prep_index(data, index, columns)
        n_rows, n_columns = data.shape
        # We need to make sure indices are sorted, as we create
        # IntIndex with no input validation (i.e. check_integrity=False ).
        # Indices may already be sorted in scipy in which case this adds
        # a small overhead.
        data.sort_indices()
        indices = data.indices
        indptr = data.indptr
        array_data = data.data
        dtype = SparseDtype(array_data.dtype)
        arrays = []
        for i in range(n_columns):
            sl = slice(indptr[i], indptr[i + 1])
            idx = IntIndex(n_rows, indices[sl], check_integrity=False)
            arr = SparseArray._simple_new(array_data[sl], idx, dtype)
            arrays.append(arr)
        return DataFrame._from_arrays(
            arrays, columns=columns, index=index, verify_integrity=False
        )

    def to_dense(self) -> DataFrame:
        """
        Convert a DataFrame with sparse values to dense.

        Returns
        -------
        DataFrame
            A DataFrame with the same values stored as dense arrays.

        See Also
        --------
        DataFrame.sparse.density : Ratio of non-sparse points to total
            (dense) data points.

        Examples
        --------
        >>> df = pd.DataFrame({"A": pd.arrays.SparseArray([0, 1, 0])})
        >>> df.sparse.to_dense()
           A
        0  0
        1  1
        2  0
        """
        data = {k: v.array.to_dense() for k, v in self._parent.items()}
        return self._parent._constructor(
            data, index=self._parent.index, columns=self._parent.columns
        )

    def to_coo(self) -> spmatrix:
        """
        Return the contents of the frame as a sparse SciPy COO matrix.

        Returns
        -------
        scipy.sparse.spmatrix
            If the caller is heterogeneous and contains booleans or objects,
            the result will be of dtype=object. See Notes.

        See Also
        --------
        DataFrame.sparse.to_dense : Convert a DataFrame with sparse values to dense.

        Notes
        -----
        The dtype will be the lowest-common-denominator type (implicit
        upcasting); that is to say if the dtypes (even of numeric types)
        are mixed, the one that accommodates all will be chosen.

        e.g. If the dtypes are float16 and float32, dtype will be upcast to
        float32. By numpy.find_common_type convention, mixing int64 and
        and uint64 will result in a float64 dtype.

        Examples
        --------
        >>> df = pd.DataFrame({"A": pd.arrays.SparseArray([0, 1, 0, 1])})
        >>> df.sparse.to_coo()
        <COOrdinate sparse matrix of dtype 'int64'
            with 2 stored elements and shape (4, 1)>
        """
        import_optional_dependency("scipy")
        from scipy.sparse import coo_matrix

        dtype = find_common_type(self._parent.dtypes.to_list())
        if isinstance(dtype, SparseDtype):
            dtype = dtype.subtype

        cols, rows, data = [], [], []
        for col, (_, ser) in enumerate(self._parent.items()):
            sp_arr = ser.array

            row = sp_arr.sp_index.indices
            cols.append(np.repeat(col, len(row)))
            rows.append(row)
            data.append(sp_arr.sp_values.astype(dtype, copy=False))

        cols = np.concatenate(cols)
        rows = np.concatenate(rows)
        data = np.concatenate(data)
        return coo_matrix((data, (rows, cols)), shape=self._parent.shape)

    @property
    def density(self) -> float:
        """
        Ratio of non-sparse points to total (dense) data points.

        See Also
        --------
        DataFrame.sparse.from_spmatrix : Create a new DataFrame from a
            scipy sparse matrix.

        Examples
        --------
        >>> df = pd.DataFrame({"A": pd.arrays.SparseArray([0, 1, 0, 1])})
        >>> df.sparse.density
        np.float64(0.5)
        """
        tmp = np.mean([column.array.density for _, column in self._parent.items()])
        return tmp

    @staticmethod
    def _prep_index(data, index, columns):
        from pandas.core.indexes.api import (
            default_index,
            ensure_index,
        )

        N, K = data.shape
        if index is None:
            index = default_index(N)
        else:
            index = ensure_index(index)
        if columns is None:
            columns = default_index(K)
        else:
            columns = ensure_index(columns)

        if len(columns) != K:
            raise ValueError(f"Column length mismatch: {len(columns)} vs. {K}")
        if len(index) != N:
            raise ValueError(f"Index length mismatch: {len(index)} vs. {N}")
        return index, columns