astro py:docs

- Index
- Modules

### Navigation

- Astropy v5.2.1 »
- Module code »
- astropy.table »

# Source code for astropy.table.bst

    # Licensed under a 3-clause BSD style license - see LICENSE.rst
    import operator

    __all__ = ["BST"]

    class MaxValue:
        """
        Represents an infinite value for purposes
        of tuple comparison.
        """

        def __gt__(self, other):
            return True

        def __ge__(self, other):
            return True

        def __lt__(self, other):
            return False

        def __le__(self, other):
            return False

        def __repr__(self):
            return "MAX"

        __str__ = __repr__

    class MinValue:
        """
        The opposite of MaxValue, i.e. a representation of
        negative infinity.
        """

        def __lt__(self, other):
            return True

        def __le__(self, other):
            return True

        def __gt__(self, other):
            return False

        def __ge__(self, other):
            return False

        def __repr__(self):
            return "MIN"

        __str__ = __repr__

    class Epsilon:
        """
        Represents the "next largest" version of a given value,
        so that for all valid comparisons we have
        x < y < Epsilon(y) < z whenever x < y < z and x, z are
        not Epsilon objects.

        Parameters
        ----------
        val : object
            Original value
        """

        __slots__ = ("val",)

        def __init__(self, val):
            self.val = val

        def __lt__(self, other):
            if self.val == other:
                return False
            return self.val < other

        def __gt__(self, other):
            if self.val == other:
                return True
            return self.val > other

        def __eq__(self, other):
            return False

        def __repr__(self):
            return repr(self.val) + " + epsilon"

    class Node:
        """
        An element in a binary search tree, containing
        a key, data, and references to children nodes and
        a parent node.

        Parameters
        ----------
        key : tuple
            Node key
        data : list or int
            Node data
        """

        __lt__ = lambda x, y: x.key < y.key
        __le__ = lambda x, y: x.key <= y.key
        __eq__ = lambda x, y: x.key == y.key
        __ge__ = lambda x, y: x.key >= y.key
        __gt__ = lambda x, y: x.key > y.key
        __ne__ = lambda x, y: x.key != y.key
        __slots__ = ("key", "data", "left", "right")

        # each node has a key and data list
        def __init__(self, key, data):
            self.key = key
            self.data = data if isinstance(data, list) else [data]
            self.left = None
            self.right = None

        def replace(self, child, new_child):
            """
            Replace this node's child with a new child.
            """
            if self.left is not None and self.left == child:
                self.left = new_child
            elif self.right is not None and self.right == child:
                self.right = new_child
            else:
                raise ValueError("Cannot call replace() on non-child")

        def remove(self, child):
            """
            Remove the given child.
            """
            self.replace(child, None)

        def set(self, other):
            """
            Copy the given node.
            """
            self.key = other.key
            self.data = other.data[:]

        def __str__(self):
            return str((self.key, self.data))

        def __repr__(self):
            return str(self)

    class BST:
        """
        A basic binary search tree in pure Python, used
        as an engine for indexing.

        Parameters
        ----------
        data : Table
            Sorted columns of the original table
        row_index : Column object
            Row numbers corresponding to data columns
        unique : bool
            Whether the values of the index must be unique.
            Defaults to False.
        """

        NodeClass = Node

        def __init__(self, data, row_index, unique=False):
            self.root = None
            self.size = 0
            self.unique = unique
            for key, row in zip(data, row_index):
                self.add(tuple(key), row)

        def add(self, key, data=None):
            """
            Add a key, data pair.
            """
            if data is None:
                data = key

            self.size += 1
            node = self.NodeClass(key, data)
            curr_node = self.root
            if curr_node is None:
                self.root = node
                return
            while True:
                if node < curr_node:
                    if curr_node.left is None:
                        curr_node.left = node
                        break
                    curr_node = curr_node.left
                elif node > curr_node:
                    if curr_node.right is None:
                        curr_node.right = node
                        break
                    curr_node = curr_node.right
                elif self.unique:
                    raise ValueError("Cannot insert non-unique value")
                else:  # add data to node
                    curr_node.data.extend(node.data)
                    curr_node.data = sorted(curr_node.data)
                    return

        def find(self, key):
            """
            Return all data values corresponding to a given key.

            Parameters
            ----------
            key : tuple
                Input key

            Returns
            -------
            data_vals : list
                List of rows corresponding to the input key
            """
            node, parent = self.find_node(key)
            return node.data if node is not None else []

        def find_node(self, key):
            """
            Find the node associated with the given key.
            """
            if self.root is None:
                return (None, None)
            return self._find_recursive(key, self.root, None)

        def shift_left(self, row):
            """
            Decrement all rows larger than the given row.
            """
            for node in self.traverse():
                node.data = [x - 1 if x > row else x for x in node.data]

        def shift_right(self, row):
            """
            Increment all rows greater than or equal to the given row.
            """
            for node in self.traverse():
                node.data = [x + 1 if x >= row else x for x in node.data]

        def _find_recursive(self, key, node, parent):
            try:
                if key == node.key:
                    return (node, parent)
                elif key > node.key:
                    if node.right is None:
                        return (None, None)
                    return self._find_recursive(key, node.right, node)
                else:
                    if node.left is None:
                        return (None, None)
                    return self._find_recursive(key, node.left, node)
            except TypeError:  # wrong key type
                return (None, None)

        def traverse(self, order="inorder"):
            """
            Return nodes of the BST in the given order.

            Parameters
            ----------
            order : str
                The order in which to recursively search the BST.
                Possible values are:
                "preorder": current node, left subtree, right subtree
                "inorder": left subtree, current node, right subtree
                "postorder": left subtree, right subtree, current node
            """
            if order == "preorder":
                return self._preorder(self.root, [])
            elif order == "inorder":
                return self._inorder(self.root, [])
            elif order == "postorder":
                return self._postorder(self.root, [])
            raise ValueError(f'Invalid traversal method: "{order}"')

        def items(self):
            """
            Return BST items in order as (key, data) pairs.
            """
            return [(x.key, x.data) for x in self.traverse()]

        def sort(self):
            """
            Make row order align with key order.
            """
            i = 0
            for node in self.traverse():
                num_rows = len(node.data)
                node.data = [x for x in range(i, i + num_rows)]
                i += num_rows

        def sorted_data(self):
            """
            Return BST rows sorted by key values.
            """
            return [x for node in self.traverse() for x in node.data]

        def _preorder(self, node, lst):
            if node is None:
                return lst
            lst.append(node)
            self._preorder(node.left, lst)
            self._preorder(node.right, lst)
            return lst

        def _inorder(self, node, lst):
            if node is None:
                return lst
            self._inorder(node.left, lst)
            lst.append(node)
            self._inorder(node.right, lst)
            return lst

        def _postorder(self, node, lst):
            if node is None:
                return lst
            self._postorder(node.left, lst)
            self._postorder(node.right, lst)
            lst.append(node)
            return lst

        def _substitute(self, node, parent, new_node):
            if node is self.root:
                self.root = new_node
            else:
                parent.replace(node, new_node)

        def remove(self, key, data=None):
            """
            Remove data corresponding to the given key.

            Parameters
            ----------
            key : tuple
                The key to remove
            data : int or None
                If None, remove the node corresponding to the given key.
                If not None, remove only the given data value from the node.

            Returns
            -------
            successful : bool
                True if removal was successful, false otherwise
            """
            node, parent = self.find_node(key)
            if node is None:
                return False
            if data is not None:
                if data not in node.data:
                    raise ValueError("Data does not belong to correct node")
                elif len(node.data) > 1:
                    node.data.remove(data)
                    return True
            if node.left is None and node.right is None:
                self._substitute(node, parent, None)
            elif node.left is None and node.right is not None:
                self._substitute(node, parent, node.right)
            elif node.right is None and node.left is not None:
                self._substitute(node, parent, node.left)
            else:
                # find largest element of left subtree
                curr_node = node.left
                parent = node
                while curr_node.right is not None:
                    parent = curr_node
                    curr_node = curr_node.right
                self._substitute(curr_node, parent, curr_node.left)
                node.set(curr_node)
            self.size -= 1
            return True

        def is_valid(self):
            """
            Returns whether this is a valid BST.
            """
            return self._is_valid(self.root)

        def _is_valid(self, node):
            if node is None:
                return True
            return (
                (node.left is None or node.left <= node)
                and (node.right is None or node.right >= node)
                and self._is_valid(node.left)
                and self._is_valid(node.right)
            )

        def range(self, lower, upper, bounds=(True, True)):
            """
            Return all nodes with keys in the given range.

            Parameters
            ----------
            lower : tuple
                Lower bound
            upper : tuple
                Upper bound
            bounds : (2,) tuple of bool
                Indicates whether the search should be inclusive or
                exclusive with respect to the endpoints. The first
                argument corresponds to an inclusive lower bound,
                and the second argument to an inclusive upper bound.
            """
            nodes = self.range_nodes(lower, upper, bounds)
            return [x for node in nodes for x in node.data]

        def range_nodes(self, lower, upper, bounds=(True, True)):
            """
            Return nodes in the given range.
            """
            if self.root is None:
                return []
            # op1 is <= or <, op2 is >= or >
            op1 = operator.le if bounds[0] else operator.lt
            op2 = operator.ge if bounds[1] else operator.gt
            return self._range(lower, upper, op1, op2, self.root, [])

        def same_prefix(self, val):
            """
            Assuming the given value has smaller length than keys, return
            nodes whose keys have this value as a prefix.
            """
            if self.root is None:
                return []
            nodes = self._same_prefix(val, self.root, [])
            return [x for node in nodes for x in node.data]

        def _range(self, lower, upper, op1, op2, node, lst):
            if op1(lower, node.key) and op2(upper, node.key):
                lst.append(node)
            if upper > node.key and node.right is not None:
                self._range(lower, upper, op1, op2, node.right, lst)
            if lower < node.key and node.left is not None:
                self._range(lower, upper, op1, op2, node.left, lst)
            return lst

        def _same_prefix(self, val, node, lst):
            prefix = node.key[: len(val)]
            if prefix == val:
                lst.append(node)
            if prefix <= val and node.right is not None:
                self._same_prefix(val, node.right, lst)
            if prefix >= val and node.left is not None:
                self._same_prefix(val, node.left, lst)
            return lst

        def __repr__(self):
            return f"<{self.__class__.__name__}>"

        def _print(self, node, level):
            line = "\t" * level + str(node) + "\n"
            if node.left is not None:
                line += self._print(node.left, level + 1)
            if node.right is not None:
                line += self._print(node.right, level + 1)
            return line

        @property
        def height(self):
            """
            Return the BST height.
            """
            return self._height(self.root)

        def _height(self, node):
            if node is None:
                return -1
            return max(self._height(node.left), self._height(node.right)) + 1

        def replace_rows(self, row_map):
            """
            Replace all rows with the values they map to in the
            given dictionary. Any rows not present as keys in
            the dictionary will have their nodes deleted.

            Parameters
            ----------
            row_map : dict
                Mapping of row numbers to new row numbers
            """
            for key, data in self.items():
                data[:] = [row_map[x] for x in data if x in row_map]