Port pandas-ts code

pyproject.toml

@@ -16,6 +16,10 @@ classifiers = [
 dynamic = ["version"]
 requires-python = ">=3.9"
 dependencies = [
+    "numpy",
+    # We use internal pd._libs.missing and experimental ArrowExtensionArray
+    "pandas>=2.2,<2.3",
+    "pyarrow>=15",
 ]
 
 [project.urls]

src/nested_pandas/__init__.py

@@ -1,3 +1,6 @@
 from .example_module import greetings, meaning
+from .series.dtype import NestedDtype
+# Import for registering
+from .series.accessor import NestSeriesAccessor  # noqa: F401
 
-__all__ = ["greetings", "meaning"]
+__all__ = ["greetings", "meaning", "NestedDtype"]

src/nested_pandas/series/accessor.py

@@ -0,0 +1,240 @@
+# Python 3.9 doesn't support "|" for types
+from __future__ import annotations
+
+from collections.abc import Generator, MutableMapping
+from typing import cast
+
+import numpy as np
+import pandas as pd
+import pyarrow as pa
+from numpy.typing import ArrayLike
+from pandas.api.extensions import register_series_accessor
+
+from nested_pandas.series.packer import pack_sorted_df_into_struct
+from nested_pandas.series.dtype import NestedDtype
+
+__all__ = ["NestSeriesAccessor"]
+
+
+@register_series_accessor("nest")
+class NestSeriesAccessor(MutableMapping):
+    """Accessor for operations on Series of NestedDtype
+
+    This accessor implements `MutableMapping` interface over the fields of the
+    struct, so you can access, change and delete the fields as if it was a
+    dictionary, with `[]`, `[] =` and `del` operators.
+    """
+
+    def __init__(self, series):
+        self._check_series(series)
+
+        self._series = series
+
+    @staticmethod
+    def _check_series(series):
+        dtype = series.dtype
+        if not isinstance(dtype, NestedDtype):
+            raise AttributeError(f"Can only use .nest accessor with a Series of NestedDtype, got {dtype}")
+
+    def to_lists(self, fields: list[str] | None = None) -> pd.DataFrame:
+        """Convert nested series into dataframe of list-array columns
+
+        Parameters
+        ----------
+        fields : list[str] or None, optional
+            Names of the fields to include. Default is None, which means all fields.
+
+        Returns
+        -------
+        pd.DataFrame
+            Dataframe of list-arrays.
+        """
+        df = self._series.struct.explode()
+        if fields is None:
+            return df
+        return df[fields]
+
+    def to_flat(self, fields: list[str] | None = None) -> pd.DataFrame:
+        """Convert nested series into dataframe of flat arrays
+
+        Parameters
+        ----------
+        fields : list[str] or None, optional
+            Names of the fields to include. Default is None, which means all fields.
+
+        Returns
+        -------
+        pd.DataFrame
+            Dataframe of flat arrays.
+        """
+        # For some reason, .struct.dtypes is cached, so we will use NestedExtensionArray directly
+        fields = fields if fields is not None else list(self._series.array.field_names)
+        if len(fields) == 0:
+            raise ValueError("Cannot flatten a struct with no fields")
+
+        flat_series = {}
+        index = None
+        for field in fields:
+            list_array = cast(pa.ListArray, pa.array(self._series.struct.field(field)))
+            if index is None:
+                index = np.repeat(self._series.index.values, np.diff(list_array.offsets))
+            flat_series[field] = pd.Series(
+                list_array.flatten(),
+                index=index,
+                name=field,
+                copy=False,
+            )
+        return pd.DataFrame(flat_series)
+
+    @property
+    def flat_length(self) -> int:
+        """Length of the flat arrays"""
+        return self._series.array.flat_length
+
+    @property
+    def fields(self) -> list[str]:
+        """Names of the nested columns"""
+        # For some reason, .struct.dtypes is cached, so we will use NestedExtensionArray directly
+        return self._series.array.field_names
+
+    def set_flat_field(self, field: str, value: ArrayLike) -> None:
+        """Set the field from flat-array of values, in-place
+
+        Parameters
+        ----------
+        field : str
+            Name of the field to set. If not present, it will be added.
+        value : ArrayLike
+            Array of values to set. It must be a scalar or have the same length
+             as the flat arrays, e.g. `self.flat_length`.
+        """
+        self._series.array.set_flat_field(field, value)
+
+    def set_list_field(self, field: str, value: ArrayLike) -> None:
+        """Set the field from list-array, in-place
+
+        Parameters
+        ----------
+        field : str
+            Name of the field to set. If not present, it will be added.
+        value : ArrayLike
+            Array of values to set. It must be a list-array of the same length
+             as the series, e.g. length of the series.
+        """
+        self._series.array.set_list_field(field, value)
+
+    # I intentionally don't call it `drop` or `drop_field` because `pd.DataFrame.drop` is not inplace
+    # by default, and I wouldn't like to surprise the user.
+    def pop_field(self, field: str) -> pd.Series:
+        """Delete the field from the struct and return it.
+
+        Parameters
+        ----------
+        field : str
+            Name of the field to delete.
+
+        Returns
+        -------
+        pd.Series
+            The deleted field.
+        """
+        series = self[field]
+        self._series.array.pop_field(field)
+        return series
+
+    def query_flat(self, query: str) -> pd.Series:
+        """Query the flat arrays with a boolean expression
+
+        Currently, it will remove empty rows from the output series.
+        # TODO: preserve the index keeping empty rows
+
+        Parameters
+        ----------
+        query : str
+            Boolean expression to filter the rows.
+
+        Returns
+        -------
+        pd.Series
+            The filtered series.
+        """
+        flat = self.to_flat().query(query)
+        if len(flat) == 0:
+            return pd.Series([], dtype=self._series.dtype)
+        return pack_sorted_df_into_struct(flat)
+
+    def get_list_series(self, field: str) -> pd.Series:
+        """Get the list-array field as a Series
+
+        Parameters
+        ----------
+        field : str
+            Name of the field to get.
+
+        Returns
+        -------
+        pd.Series
+            The list-array field.
+        """
+        return self._series.struct.field(field)
+
+    def __getitem__(self, key: str | list[str]) -> pd.Series:
+        if isinstance(key, list):
+            new_array = self._series.array.view_fields(key)
+            return pd.Series(new_array, index=self._series.index, name=self._series.name)
+
+        series = self._series.struct.field(key).list.flatten()
+        series.index = np.repeat(self._series.index.values, np.diff(self._series.array.list_offsets))
+        series.name = key
+        return series
+
+    def __setitem__(self, key: str, value: ArrayLike) -> None:
+        # TODO: we can be much-much smarter about the performance here
+        # TODO: think better about underlying pa.ChunkArray in both self._series.array and value
+
+        # Everything is empty, do nothing
+        if len(self._series) == 0 and np.ndim(value) != 0:
+            array = pa.array(value)
+            if len(array) == 0:
+                return
+
+        if len(self._series) == self.flat_length:
+            raise ValueError(
+                f"Cannot use `.nest[{key}] = value` when the series has the same count of 'list' rows as"
+                "'flat' rows, because it is ambiguous whether the input is a 'flat' or a 'list' array. Use"
+                "`.nest.set_flat_field()` or `.nest.set_list_field()` instead."
+            )
+
+        # Set single value for all rows
+        if np.ndim(value) == 0:
+            self.set_flat_field(key, value)
+            return
+
+        pa_array = pa.array(value)
+
+        # Input is a flat array of values
+        if len(pa_array) == self.flat_length:
+            self.set_flat_field(key, pa_array)
+            return
+
+        # Input is a list-array of values
+        if len(pa_array) == len(self._series):
+            self.set_list_field(key, pa_array)
+            return
+
+        raise ValueError(
+            f"Cannot set field {key} with value of length {len(pa_array)}, the value is expected to be "
+            f"either a scalar, a 'flat' array of length {self.flat_length}, or a 'list' array of length "
+            f"{len(self._series)}."
+        )
+
+    def __delitem__(self, key: str) -> None:
+        self.pop_field(key)
+
+    def __iter__(self) -> Generator[str, None, None]:
+        # For some reason, .struct.dtypes is cached, so we will use NestedExtensionArray directly
+        yield from iter(self._series.array.field_names)
+
+    def __len__(self) -> int:
+        # For some reason, .struct.dtypes is cached, so we will use NestedExtensionArray directly
+        return len(self._series.array.field_names)