"""
Low-dependency indexing utilities.
"""
import warnings
import numpy as np
from pandas._typing import Any, AnyArrayLike
from pandas.core.dtypes.common import (
is_array_like,
is_bool_dtype,
is_extension_array_dtype,
is_integer,
is_integer_dtype,
is_list_like,
)
from pandas.core.dtypes.generic import ABCIndexClass, ABCSeries
# -----------------------------------------------------------
# Indexer Identification
def is_valid_positional_slice(slc: slice) -> bool:
"""
Check if a slice object can be interpreted as a positional indexer.
Parameters
----------
slc : slice
Returns
-------
bool
Notes
-----
A valid positional slice may also be interpreted as a label-based slice
depending on the index being sliced.
"""
def is_int_or_none(val):
return val is None or is_integer(val)
return (
is_int_or_none(slc.start)
and is_int_or_none(slc.stop)
and is_int_or_none(slc.step)
)
def is_list_like_indexer(key) -> bool:
"""
Check if we have a list-like indexer that is *not* a NamedTuple.
Parameters
----------
key : object
Returns
-------
bool
"""
# allow a list_like, but exclude NamedTuples which can be indexers
return is_list_like(key) and not (isinstance(key, tuple) and type(key) is not tuple)
def is_scalar_indexer(indexer, ndim: int) -> bool:
"""
Return True if we are all scalar indexers.
Parameters
----------
indexer : object
ndim : int
Number of dimensions in the object being indexed.
Returns
-------
bool
"""
if isinstance(indexer, tuple):
if len(indexer) == ndim:
return all(
is_integer(x) or (isinstance(x, np.ndarray) and x.ndim == len(x) == 1)
for x in indexer
)
return False
def is_empty_indexer(indexer, arr_value: np.ndarray) -> bool:
"""
Check if we have an empty indexer.
Parameters
----------
indexer : object
arr_value : np.ndarray
Returns
-------
bool
"""
if is_list_like(indexer) and not len(indexer):
return True
if arr_value.ndim == 1:
if not isinstance(indexer, tuple):
indexer = tuple([indexer])
return any(isinstance(idx, np.ndarray) and len(idx) == 0 for idx in indexer)
return False
# -----------------------------------------------------------
# Indexer Validation
def check_setitem_lengths(indexer, value, values) -> None:
"""
Validate that value and indexer are the same length.
An special-case is allowed for when the indexer is a boolean array
and the number of true values equals the length of ``value``. In
this case, no exception is raised.
Parameters
----------
indexer : sequence
Key for the setitem.
value : array-like
Value for the setitem.
values : array-like
Values being set into.
Returns
-------
None
Raises
------
ValueError
When the indexer is an ndarray or list and the lengths don't match.
"""
# boolean with truth values == len of the value is ok too
if isinstance(indexer, (np.ndarray, list)):
if is_list_like(value) and len(indexer) != len(value):
if not (
isinstance(indexer, np.ndarray)
and indexer.dtype == np.bool_
and len(indexer[indexer]) == len(value)
):
raise ValueError(
"cannot set using a list-like indexer "
"with a different length than the value"
)
elif isinstance(indexer, slice):
# slice
if is_list_like(value) and len(values):
if len(value) != length_of_indexer(indexer, values):
raise ValueError(
"cannot set using a slice indexer with a "
"different length than the value"
)
def validate_indices(indices: np.ndarray, n: int) -> None:
"""
Perform bounds-checking for an indexer.
-1 is allowed for indicating missing values.
Parameters
----------
indices : ndarray
n : int
Length of the array being indexed.
Raises
------
ValueError
Examples
--------
>>> validate_indices([1, 2], 3)
# OK
>>> validate_indices([1, -2], 3)
ValueError
>>> validate_indices([1, 2, 3], 3)
IndexError
>>> validate_indices([-1, -1], 0)
# OK
>>> validate_indices([0, 1], 0)
IndexError
"""
if len(indices):
min_idx = indices.min()
if min_idx < -1:
msg = f"'indices' contains values less than allowed ({min_idx} < -1)"
raise ValueError(msg)
max_idx = indices.max()
if max_idx >= n:
raise IndexError("indices are out-of-bounds")
# -----------------------------------------------------------
# Indexer Conversion
def maybe_convert_indices(indices, n: int):
"""
Attempt to convert indices into valid, positive indices.
If we have negative indices, translate to positive here.
If we have indices that are out-of-bounds, raise an IndexError.
Parameters
----------
indices : array-like
Array of indices that we are to convert.
n : int
Number of elements in the array that we are indexing.
Returns
-------
array-like
An array-like of positive indices that correspond to the ones
that were passed in initially to this function.
Raises
------
IndexError
One of the converted indices either exceeded the number of,
elements (specified by `n`), or was still negative.
"""
if isinstance(indices, list):
indices = np.array(indices)
if len(indices) == 0:
# If `indices` is empty, np.array will return a float,
# and will cause indexing errors.
return np.empty(0, dtype=np.intp)
mask = indices < 0
if mask.any():
indices = indices.copy()
indices[mask] += n
mask = (indices >= n) | (indices < 0)
if mask.any():
raise IndexError("indices are out-of-bounds")
return indices
# -----------------------------------------------------------
# Unsorted
def length_of_indexer(indexer, target=None) -> int:
"""
Return the expected length of target[indexer]
Returns
-------
int
"""
if target is not None and isinstance(indexer, slice):
target_len = len(target)
start = indexer.start
stop = indexer.stop
step = indexer.step
if start is None:
start = 0
elif start < 0:
start += target_len
if stop is None or stop > target_len:
stop = target_len
elif stop < 0:
stop += target_len
if step is None:
step = 1
elif step < 0:
start, stop = stop + 1, start + 1
step = -step
return (stop - start + step - 1) // step
elif isinstance(indexer, (ABCSeries, ABCIndexClass, np.ndarray, list)):
if isinstance(indexer, list):
indexer = np.array(indexer)
if indexer.dtype == bool:
# GH#25774
return indexer.sum()
return len(indexer)
elif not is_list_like_indexer(indexer):
return 1
raise AssertionError("cannot find the length of the indexer")
def deprecate_ndim_indexing(result, stacklevel=3):
"""
Helper function to raise the deprecation warning for multi-dimensional
indexing on 1D Series/Index.
GH#27125 indexer like idx[:, None] expands dim, but we cannot do that
and keep an index, so we currently return ndarray, which is deprecated
(Deprecation GH#30588).
"""
if np.ndim(result) > 1:
warnings.warn(
"Support for multi-dimensional indexing (e.g. `obj[:, None]`) "
"is deprecated and will be removed in a future "
"version. Convert to a numpy array before indexing instead.",
FutureWarning,
stacklevel=stacklevel,
)
def unpack_1tuple(tup):
"""
If we have a length-1 tuple/list that contains a slice, unpack to just
the slice.
Notes
-----
The list case is deprecated.
"""
if len(tup) == 1 and isinstance(tup[0], slice):
# if we don't have a MultiIndex, we may still be able to handle
# a 1-tuple. see test_1tuple_without_multiindex
if isinstance(tup, list):
# GH#31299
warnings.warn(
"Indexing with a single-item list containing a "
"slice is deprecated and will raise in a future "
"version. Pass a tuple instead.",
FutureWarning,
stacklevel=3,
)
return tup[0]
return tup
# -----------------------------------------------------------
# Public indexer validation
def check_array_indexer(array: AnyArrayLike, indexer: Any) -> Any:
"""
Check if `indexer` is a valid array indexer for `array`.
For a boolean mask, `array` and `indexer` are checked to have the same
length. The dtype is validated, and if it is an integer or boolean
ExtensionArray, it is checked if there are missing values present, and
it is converted to the appropriate numpy array. Other dtypes will raise
an error.
Non-array indexers (integer, slice, Ellipsis, tuples, ..) are passed
through as is.
.. versionadded:: 1.0.0
Parameters
----------
array : array-like
The array that is being indexed (only used for the length).
indexer : array-like or list-like
The array-like that's used to index. List-like input that is not yet
a numpy array or an ExtensionArray is converted to one. Other input
types are passed through as is.
Returns
-------
numpy.ndarray
The validated indexer as a numpy array that can be used to index.
Raises
------
IndexError
When the lengths don't match.
ValueError
When `indexer` cannot be converted to a numpy ndarray to index
(e.g. presence of missing values).
See Also
--------
api.types.is_bool_dtype : Check if `key` is of boolean dtype.
Examples
--------
When checking a boolean mask, a boolean ndarray is returned when the
arguments are all valid.
>>> mask = pd.array([True, False])
>>> arr = pd.array([1, 2])
>>> pd.api.indexers.check_array_indexer(arr, mask)
array([ True, False])
An IndexError is raised when the lengths don't match.
>>> mask = pd.array([True, False, True])
>>> pd.api.indexers.check_array_indexer(arr, mask)
Traceback (most recent call last):
...
IndexError: Boolean index has wrong length: 3 instead of 2.
NA values in a boolean array are treated as False.
>>> mask = pd.array([True, pd.NA])
>>> pd.api.indexers.check_array_indexer(arr, mask)
array([ True, False])
A numpy boolean mask will get passed through (if the length is correct):
>>> mask = np.array([True, False])
>>> pd.api.indexers.check_array_indexer(arr, mask)
array([ True, False])
Similarly for integer indexers, an integer ndarray is returned when it is
a valid indexer, otherwise an error is (for integer indexers, a matching
length is not required):
>>> indexer = pd.array([0, 2], dtype="Int64")
>>> arr = pd.array([1, 2, 3])
>>> pd.api.indexers.check_array_indexer(arr, indexer)
array([0, 2])
>>> indexer = pd.array([0, pd.NA], dtype="Int64")
>>> pd.api.indexers.check_array_indexer(arr, indexer)
Traceback (most recent call last):
...
ValueError: Cannot index with an integer indexer containing NA values
For non-integer/boolean dtypes, an appropriate error is raised:
>>> indexer = np.array([0., 2.], dtype="float64")
>>> pd.api.indexers.check_array_indexer(arr, indexer)
Traceback (most recent call last):
...
IndexError: arrays used as indices must be of integer or boolean type
"""
from pandas.core.construction import array as pd_array
# whatever is not an array-like is returned as-is (possible valid array
# indexers that are not array-like: integer, slice, Ellipsis, None)
# In this context, tuples are not considered as array-like, as they have
# a specific meaning in indexing (multi-dimensional indexing)
if is_list_like(indexer):
if isinstance(indexer, tuple):
return indexer
else:
return indexer
# convert list-likes to array
if not is_array_like(indexer):
indexer = pd_array(indexer)
if len(indexer) == 0:
# empty list is converted to float array by pd.array
indexer = np.array([], dtype=np.intp)
dtype = indexer.dtype
if is_bool_dtype(dtype):
if is_extension_array_dtype(dtype):
indexer = indexer.to_numpy(dtype=bool, na_value=False)
else:
indexer = np.asarray(indexer, dtype=bool)
# GH26658
if len(indexer) != len(array):
raise IndexError(
f"Boolean index has wrong length: "
f"{len(indexer)} instead of {len(array)}"
)
elif is_integer_dtype(dtype):
try:
indexer = np.asarray(indexer, dtype=np.intp)
except ValueError as err:
raise ValueError(
"Cannot index with an integer indexer containing NA values"
) from err
else:
raise IndexError("arrays used as indices must be of integer or boolean type")
return indexer