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index.py
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index.py
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# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Indexing for Table columns.
The Index class can use several implementations as its
engine. Any implementation should implement the following:
__init__(data, row_index) : initialize index based on key/row list pairs
add(key, row) -> None : add (key, row) to existing data
remove(key, data=None) -> boolean : remove data from self[key], or all of
self[key] if data is None
shift_left(row) -> None : decrement row numbers after row
shift_right(row) -> None : increase row numbers >= row
find(key) -> list : list of rows corresponding to key
range(lower, upper, bounds) -> list : rows in self[k] where k is between
lower and upper (<= or < based on bounds)
sort() -> None : make row order align with key order
sorted_data() -> list of rows in sorted order (by key)
replace_rows(row_map) -> None : replace row numbers based on slice
items() -> list of tuples of the form (key, data)
Notes
-----
When a Table is initialized from another Table, indices are
(deep) copied and their columns are set to the columns of the new Table.
Column creation:
Column(c) -> deep copy of indices
c[[1, 2]] -> deep copy and reordering of indices
c[1:2] -> reference
array.view(Column) -> no indices
"""
from copy import deepcopy
import numpy as np
from .bst import MaxValue, MinValue
from .sorted_array import SortedArray
class QueryError(ValueError):
"""
Indicates that a given index cannot handle the supplied query.
"""
class Index:
"""
The Index class makes it possible to maintain indices
on columns of a Table, so that column values can be queried
quickly and efficiently. Column values are stored in lexicographic
sorted order, which allows for binary searching in O(log n).
Parameters
----------
columns : list or None
List of columns on which to create an index. If None,
create an empty index for purposes of deep copying.
engine : type, instance, or None
Indexing engine class to use (from among SortedArray, BST,
and SCEngine) or actual engine instance.
If the supplied argument is None (by default), use SortedArray.
unique : bool (defaults to False)
Whether the values of the index must be unique
"""
def __init__(self, columns, engine=None, unique=False):
# Local imports to avoid import problems.
from astropy.time import Time
from .table import Column, Table
if columns is not None:
columns = list(columns)
if engine is not None and not isinstance(engine, type):
# create from data
self.engine = engine.__class__
self.data = engine
self.columns = columns
return
# by default, use SortedArray
self.engine = engine or SortedArray
if columns is None: # this creates a special exception for deep copying
columns = []
data = []
row_index = []
elif len(columns) == 0:
raise ValueError("Cannot create index without at least one column")
elif len(columns) == 1:
col = columns[0]
row_index = Column(col.argsort(kind="stable"))
data = Table([col[row_index]])
else:
num_rows = len(columns[0])
# replace Time columns with approximate form and remainder
new_columns = []
for col in columns:
if isinstance(col, Time):
new_columns.append(col.jd)
remainder = col - col.__class__(
col.jd, format="jd", scale=col.scale
)
new_columns.append(remainder.jd)
else:
new_columns.append(col)
# sort the table lexicographically and keep row numbers
table = Table(columns + [np.arange(num_rows)], copy_indices=False)
sort_columns = new_columns[::-1]
try:
lines = table[np.lexsort(sort_columns)]
except TypeError: # arbitrary mixins might not work with lexsort
lines = table[table.argsort(kind="stable")]
data = lines[lines.colnames[:-1]]
row_index = lines[lines.colnames[-1]]
self.data = self.engine(data, row_index, unique=unique)
self.columns = columns
def __len__(self):
"""
Number of rows in index.
"""
return len(self.columns[0])
def replace_col(self, prev_col, new_col):
"""
Replace an indexed column with an updated reference.
Parameters
----------
prev_col : Column
Column reference to replace
new_col : Column
New column reference
"""
self.columns[self.col_position(prev_col.info.name)] = new_col
def reload(self):
"""
Recreate the index based on data in self.columns.
"""
self.__init__(self.columns, engine=self.engine)
def col_position(self, col_name):
"""
Return the position of col_name in self.columns.
Parameters
----------
col_name : str
Name of column to look up
"""
for i, c in enumerate(self.columns):
if c.info.name == col_name:
return i
raise ValueError(f"Column does not belong to index: {col_name}")
def insert_row(self, pos, vals, columns):
"""
Insert a new row from the given values.
Parameters
----------
pos : int
Position at which to insert row
vals : list or tuple
List of values to insert into a new row
columns : list
Table column references
"""
key = [None] * len(self.columns)
for i, col in enumerate(columns):
try:
key[self.col_position(col.info.name)] = vals[i]
except ValueError: # not a member of index
continue
num_rows = len(self.columns[0])
if pos < num_rows:
# shift all rows >= pos to the right
self.data.shift_right(pos)
self.data.add(tuple(key), pos)
def get_row_specifier(self, row_specifier):
"""
Return an iterable corresponding to the
input row specifier.
Parameters
----------
row_specifier : int, list, ndarray, or slice
"""
if isinstance(row_specifier, (int, np.integer)):
# single row
return (row_specifier,)
elif isinstance(row_specifier, (list, np.ndarray)):
return row_specifier
elif isinstance(row_specifier, slice):
col_len = len(self.columns[0])
return range(*row_specifier.indices(col_len))
raise ValueError(
"Expected int, array of ints, or slice but got {} in remove_rows".format(
row_specifier
)
)
def remove_rows(self, row_specifier):
"""
Remove the given rows from the index.
Parameters
----------
row_specifier : int, list, ndarray, or slice
Indicates which row(s) to remove
"""
rows = []
# To maintain the correct row order, we loop twice,
# deleting rows first and then reordering the remaining rows
for row in self.get_row_specifier(row_specifier):
self.remove_row(row, reorder=False)
rows.append(row)
# second pass - row order is reversed to maintain
# correct row numbers
for row in sorted(rows, reverse=True):
self.data.shift_left(row)
def remove_row(self, row, reorder=True):
"""
Remove the given row from the index.
Parameters
----------
row : int
Position of row to remove
reorder : bool
Whether to reorder indices after removal
"""
# for removal, form a key consisting of column values in this row
if not self.data.remove(tuple(col[row] for col in self.columns), row):
raise ValueError(f"Could not remove row {row} from index")
# decrement the row number of all later rows
if reorder:
self.data.shift_left(row)
def find(self, key):
"""
Return the row values corresponding to key, in sorted order.
Parameters
----------
key : tuple
Values to search for in each column
"""
return self.data.find(key)
def same_prefix(self, key):
"""
Return rows whose keys contain the supplied key as a prefix.
Parameters
----------
key : tuple
Prefix for which to search
"""
return self.same_prefix_range(key, key, (True, True))
def same_prefix_range(self, lower, upper, bounds=(True, True)):
"""
Return rows whose keys have a prefix in the given range.
Parameters
----------
lower : tuple
Lower prefix bound
upper : tuple
Upper prefix bound
bounds : tuple (x, y) of bools
Indicates whether the search should be inclusive or
exclusive with respect to the endpoints. The first
argument x corresponds to an inclusive lower bound,
and the second argument y to an inclusive upper bound.
"""
n = len(lower)
ncols = len(self.columns)
a = MinValue() if bounds[0] else MaxValue()
b = MaxValue() if bounds[1] else MinValue()
# [x, y] search corresponds to [(x, min), (y, max)]
# (x, y) search corresponds to ((x, max), (x, min))
lower = lower + tuple((ncols - n) * [a])
upper = upper + tuple((ncols - n) * [b])
return self.data.range(lower, upper, bounds)
def range(self, lower, upper, bounds=(True, True)):
"""
Return rows within the given range.
Parameters
----------
lower : tuple
Lower prefix bound
upper : tuple
Upper prefix bound
bounds : tuple (x, y) of bools
Indicates whether the search should be inclusive or
exclusive with respect to the endpoints. The first
argument x corresponds to an inclusive lower bound,
and the second argument y to an inclusive upper bound.
"""
return self.data.range(lower, upper, bounds)
def replace(self, row, col_name, val):
"""
Replace the value of a column at a given position.
Parameters
----------
row : int
Row number to modify
col_name : str
Name of the Column to modify
val : col.info.dtype
Value to insert at specified row of col
"""
self.remove_row(row, reorder=False)
key = [c[row] for c in self.columns]
key[self.col_position(col_name)] = val
self.data.add(tuple(key), row)
def replace_rows(self, col_slice):
"""
Modify rows in this index to agree with the specified
slice. For example, given an index
{'5': 1, '2': 0, '3': 2} on a column ['2', '5', '3'],
an input col_slice of [2, 0] will result in the relabeling
{'3': 0, '2': 1} on the sliced column ['3', '2'].
Parameters
----------
col_slice : list
Indices to slice
"""
row_map = {row: i for i, row in enumerate(col_slice)}
self.data.replace_rows(row_map)
def sort(self):
"""
Make row numbers follow the same sort order as the keys
of the index.
"""
self.data.sort()
def sorted_data(self):
"""
Returns a list of rows in sorted order based on keys;
essentially acts as an argsort() on columns.
"""
return self.data.sorted_data()
def __getitem__(self, item):
"""
Returns a sliced version of this index.
Parameters
----------
item : slice
Input slice
Returns
-------
SlicedIndex
A sliced reference to this index.
"""
return SlicedIndex(self, item)
def __repr__(self):
col_names = tuple(col.info.name for col in self.columns)
return f"<{self.__class__.__name__} columns={col_names} data={self.data}>"
def __deepcopy__(self, memo):
"""
Return a deep copy of this index.
Notes
-----
The default deep copy must be overridden to perform
a shallow copy of the index columns, avoiding infinite recursion.
Parameters
----------
memo : dict
"""
# Bypass Index.__new__ to create an actual Index, not a SlicedIndex.
index = super().__new__(self.__class__)
index.__init__(None, engine=self.engine)
index.data = deepcopy(self.data, memo)
index.columns = self.columns[:] # new list, same columns
memo[id(self)] = index
return index
class SlicedIndex:
"""
This class provides a wrapper around an actual Index object
to make index slicing function correctly. Since numpy expects
array slices to provide an actual data view, a SlicedIndex should
retrieve data directly from the original index and then adapt
it to the sliced coordinate system as appropriate.
Parameters
----------
index : Index
The original Index reference
index_slice : tuple, slice
The slice to which this SlicedIndex corresponds
original : bool
Whether this SlicedIndex represents the original index itself.
For the most part this is similar to index[:] but certain
copying operations are avoided, and the slice retains the
length of the actual index despite modification.
"""
def __init__(self, index, index_slice, original=False):
self.index = index
self.original = original
self._frozen = False
if isinstance(index_slice, tuple):
self.start, self._stop, self.step = index_slice
elif isinstance(index_slice, slice): # index_slice is an actual slice
num_rows = len(index.columns[0])
self.start, self._stop, self.step = index_slice.indices(num_rows)
else:
raise TypeError("index_slice must be tuple or slice")
@property
def length(self):
return 1 + (self.stop - self.start - 1) // self.step
@property
def stop(self):
"""
The stopping position of the slice, or the end of the
index if this is an original slice.
"""
return len(self.index) if self.original else self._stop
def __getitem__(self, item):
"""
Returns another slice of this Index slice.
Parameters
----------
item : slice
Index slice
"""
if self.length <= 0:
# empty slice
return SlicedIndex(self.index, slice(1, 0))
start, stop, step = item.indices(self.length)
new_start = self.orig_coords(start)
new_stop = self.orig_coords(stop)
new_step = self.step * step
return SlicedIndex(self.index, (new_start, new_stop, new_step))
def sliced_coords(self, rows):
"""
Convert the input rows to the sliced coordinate system.
Parameters
----------
rows : list
Rows in the original coordinate system
Returns
-------
sliced_rows : list
Rows in the sliced coordinate system
"""
if self.original:
return rows
else:
rows = np.array(rows)
row0 = rows - self.start
if self.step != 1:
correct_mod = np.mod(row0, self.step) == 0
row0 = row0[correct_mod]
if self.step > 0:
ok = (row0 >= 0) & (row0 < self.stop - self.start)
else:
ok = (row0 <= 0) & (row0 > self.stop - self.start)
return row0[ok] // self.step
def orig_coords(self, row):
"""
Convert the input row from sliced coordinates back
to original coordinates.
Parameters
----------
row : int
Row in the sliced coordinate system
Returns
-------
orig_row : int
Row in the original coordinate system
"""
return row if self.original else self.start + row * self.step
def find(self, key):
return self.sliced_coords(self.index.find(key))
def where(self, col_map):
return self.sliced_coords(self.index.where(col_map))
def range(self, lower, upper):
return self.sliced_coords(self.index.range(lower, upper))
def same_prefix(self, key):
return self.sliced_coords(self.index.same_prefix(key))
def sorted_data(self):
return self.sliced_coords(self.index.sorted_data())
def replace(self, row, col, val):
if not self._frozen:
self.index.replace(self.orig_coords(row), col, val)
def get_index_or_copy(self):
if not self.original:
# replace self.index with a new object reference
self.index = deepcopy(self.index)
return self.index
def insert_row(self, pos, vals, columns):
if not self._frozen:
self.get_index_or_copy().insert_row(self.orig_coords(pos), vals, columns)
def get_row_specifier(self, row_specifier):
return [
self.orig_coords(x) for x in self.index.get_row_specifier(row_specifier)
]
def remove_rows(self, row_specifier):
if not self._frozen:
self.get_index_or_copy().remove_rows(row_specifier)
def replace_rows(self, col_slice):
if not self._frozen:
self.index.replace_rows([self.orig_coords(x) for x in col_slice])
def sort(self):
if not self._frozen:
self.get_index_or_copy().sort()
def __repr__(self):
slice_str = (
"" if self.original else f" slice={self.start}:{self.stop}:{self.step}"
)
return (
f"<{self.__class__.__name__} original={self.original}{slice_str}"
f" index={self.index}>"
)
def replace_col(self, prev_col, new_col):
self.index.replace_col(prev_col, new_col)
def reload(self):
self.index.reload()
def col_position(self, col_name):
return self.index.col_position(col_name)
def get_slice(self, col_slice, item):
"""
Return a newly created index from the given slice.
Parameters
----------
col_slice : Column object
Already existing slice of a single column
item : list or ndarray
Slice for retrieval
"""
from .table import Table
if len(self.columns) == 1:
index = Index([col_slice], engine=self.data.__class__)
return self.__class__(index, slice(0, 0, None), original=True)
t = Table(self.columns, copy_indices=False)
with t.index_mode("discard_on_copy"):
new_cols = t[item].columns.values()
index = Index(new_cols, engine=self.data.__class__)
return self.__class__(index, slice(0, 0, None), original=True)
@property
def columns(self):
return self.index.columns
@property
def data(self):
return self.index.data
def get_index(table, table_copy=None, names=None):
"""
Inputs a table and some subset of its columns as table_copy.
List or tuple containing names of columns as names,and returns an index
corresponding to this subset or list or None if no such index exists.
Parameters
----------
table : `Table`
Input table
table_copy : `Table`, optional
Subset of the columns in the ``table`` argument
names : list, tuple, optional
Subset of column names in the ``table`` argument
Returns
-------
Index of columns or None
"""
if names is not None and table_copy is not None:
raise ValueError(
'one and only one argument from "table_copy" or "names" is required'
)
if names is None and table_copy is None:
raise ValueError(
'one and only one argument from "table_copy" or "names" is required'
)
if names is not None:
names = set(names)
else:
names = set(table_copy.colnames)
if not names <= set(table.colnames):
raise ValueError(f"{names} is not a subset of table columns")
for name in names:
for index in table[name].info.indices:
if {col.info.name for col in index.columns} == names:
return index
return None
def get_index_by_names(table, names):
"""
Returns an index in ``table`` corresponding to the ``names`` columns or None
if no such index exists.
Parameters
----------
table : `Table`
Input table
nmaes : tuple, list
Column names
"""
names = list(names)
for index in table.indices:
index_names = [col.info.name for col in index.columns]
if index_names == names:
return index
return None
class _IndexModeContext:
"""
A context manager that allows for special indexing modes, which
are intended to improve performance. Currently the allowed modes
are "freeze", in which indices are not modified upon column modification,
"copy_on_getitem", in which indices are copied upon column slicing,
and "discard_on_copy", in which indices are discarded upon table
copying/slicing.
"""
_col_subclasses = {}
def __init__(self, table, mode):
"""
Parameters
----------
table : Table
The table to which the mode should be applied
mode : str
Either 'freeze', 'copy_on_getitem', or 'discard_on_copy'.
In 'discard_on_copy' mode,
indices are not copied whenever columns or tables are copied.
In 'freeze' mode, indices are not modified whenever columns are
modified; at the exit of the context, indices refresh themselves
based on column values. This mode is intended for scenarios in
which one intends to make many additions or modifications on an
indexed column.
In 'copy_on_getitem' mode, indices are copied when taking column
slices as well as table slices, so col[i0:i1] will preserve
indices.
"""
self.table = table
self.mode = mode
# Used by copy_on_getitem
self._orig_classes = []
if mode not in ("freeze", "discard_on_copy", "copy_on_getitem"):
raise ValueError(
"Expected a mode of either 'freeze', "
"'discard_on_copy', or 'copy_on_getitem', got "
f"'{mode}'"
)
def __enter__(self):
if self.mode == "discard_on_copy":
self.table._copy_indices = False
elif self.mode == "copy_on_getitem":
for col in self.table.columns.values():
self._orig_classes.append(col.__class__)
col.__class__ = self._get_copy_on_getitem_shim(col.__class__)
else:
for index in self.table.indices:
index._frozen = True
def __exit__(self, exc_type, exc_value, traceback):
if self.mode == "discard_on_copy":
self.table._copy_indices = True
elif self.mode == "copy_on_getitem":
for col in reversed(self.table.columns.values()):
col.__class__ = self._orig_classes.pop()
else:
for index in self.table.indices:
index._frozen = False
index.reload()
def _get_copy_on_getitem_shim(self, cls):
"""
This creates a subclass of the column's class which overrides that
class's ``__getitem__``, such that when returning a slice of the
column, the relevant indices are also copied over to the slice.
Ideally, rather than shimming in a new ``__class__`` we would be able
to just flip a flag that is checked by the base class's
``__getitem__``. Unfortunately, since the flag needs to be a Python
variable, this slows down ``__getitem__`` too much in the more common
case where a copy of the indices is not needed. See the docstring for
``astropy.table._column_mixins`` for more information on that.
"""
if cls in self._col_subclasses:
return self._col_subclasses[cls]
def __getitem__(self, item):
value = cls.__getitem__(self, item)
if type(value) is type(self):
value = self.info.slice_indices(value, item, len(self))
return value
clsname = f"_{cls.__name__}WithIndexCopy"
new_cls = type(str(clsname), (cls,), {"__getitem__": __getitem__})
self._col_subclasses[cls] = new_cls
return new_cls
class TableIndices(list):
"""
A special list of table indices allowing
for retrieval by column name(s).
Parameters
----------
lst : list
List of indices
"""
def __init__(self, lst):
super().__init__(lst)
def __getitem__(self, item):
"""
Retrieve an item from the list of indices.
Parameters
----------
item : int, str, tuple, or list
Position in list or name(s) of indexed column(s)
"""
if isinstance(item, str):
item = [item]
if isinstance(item, (list, tuple)):
item = list(item)
for index in self:
try:
for name in item:
index.col_position(name)
if len(index.columns) == len(item):
return index
except ValueError:
pass
# index search failed
raise IndexError(f"No index found for {item}")
return super().__getitem__(item)
class TableLoc:
"""
A pseudo-list of Table rows allowing for retrieval
of rows by indexed column values.
Parameters
----------
table : Table
Indexed table to use
"""
def __init__(self, table):
self.table = table
self.indices = table.indices
if len(self.indices) == 0:
raise ValueError("Cannot create TableLoc object with no indices")
def _get_rows(self, item):
"""
Retrieve Table rows indexes by value slice.
"""
if isinstance(item, tuple):
key, item = item
else:
key = self.table.primary_key
index = self.indices[key]
if len(index.columns) > 1:
raise ValueError("Cannot use .loc on multi-column indices")
if isinstance(item, slice):
# None signifies no upper/lower bound
start = MinValue() if item.start is None else item.start
stop = MaxValue() if item.stop is None else item.stop
rows = index.range((start,), (stop,))
else:
if not isinstance(item, (list, np.ndarray)): # single element
item = [item]
# item should be a list or ndarray of values
rows = []
for key in item:
p = index.find((key,))
if len(p) == 0:
raise KeyError(f"No matches found for key {key}")
else:
rows.extend(p)
return rows
def __getitem__(self, item):
"""
Retrieve Table rows by value slice.
Parameters
----------
item : column element, list, ndarray, slice or tuple
Can be a value of the table primary index, a list/ndarray
of such values, or a value slice (both endpoints are included).
If a tuple is provided, the first element must be
an index to use instead of the primary key, and the
second element must be as above.
"""
rows = self._get_rows(item)
if len(rows) == 0: # no matches found
raise KeyError(f"No matches found for key {item}")
elif len(rows) == 1: # single row
return self.table[rows[0]]
return self.table[rows]
def __setitem__(self, key, value):
"""
Assign Table row's by value slice.
Parameters
----------
key : column element, list, ndarray, slice or tuple
Can be a value of the table primary index, a list/ndarray
of such values, or a value slice (both endpoints are included).
If a tuple is provided, the first element must be
an index to use instead of the primary key, and the
second element must be as above.
value : New values of the row elements.
Can be a list of tuples/lists to update the row.
"""
rows = self._get_rows(key)
if len(rows) == 0: # no matches found
raise KeyError(f"No matches found for key {key}")
elif len(rows) == 1: # single row
self.table[rows[0]] = value
else: # multiple rows
if len(rows) == len(value):
for row, val in zip(rows, value):
self.table[row] = val
else:
raise ValueError(f"Right side should contain {len(rows)} values")
class TableLocIndices(TableLoc):
def __getitem__(self, item):
"""
Retrieve Table row's indices by value slice.
Parameters
----------
item : column element, list, ndarray, slice or tuple
Can be a value of the table primary index, a list/ndarray
of such values, or a value slice (both endpoints are included).
If a tuple is provided, the first element must be
an index to use instead of the primary key, and the
second element must be as above.
"""
rows = self._get_rows(item)
if len(rows) == 0: # no matches found
raise KeyError(f"No matches found for key {item}")
elif len(rows) == 1: # single row
return rows[0]
return rows
class TableILoc(TableLoc):
"""
A variant of TableLoc allowing for row retrieval by
indexed order rather than data values.
Parameters
----------
table : Table
Indexed table to use
"""
def __init__(self, table):
super().__init__(table)
def __getitem__(self, item):
if isinstance(item, tuple):
key, item = item
else:
key = self.table.primary_key
index = self.indices[key]
rows = index.sorted_data()[item]
table_slice = self.table[rows]
if len(table_slice) == 0: # no matches found
raise IndexError(f"Invalid index for iloc: {item}")
return table_slice