CLN: remove unused parts of skiplist (most of it) (pandas-dev#27465)

Author: jbrockmendel

pandas/_libs/skiplist.pxd

@@ -1,7 +1,5 @@
 # -*- coding: utf-8 -*-
-
-from cython cimport Py_ssize_t
-
+# See GH#27465 for reference on related-but-unused cython code
 
 cdef extern from "src/skiplist.h":
     ctypedef struct node_t:
@@ -24,22 +22,3 @@ cdef extern from "src/skiplist.h":
     double skiplist_get(skiplist_t*, int, int*) nogil
     int skiplist_insert(skiplist_t*, double) nogil
     int skiplist_remove(skiplist_t*, double) nogil
-
-
-# Note: Node is declared here so that IndexableSkiplist can be exposed;
-# Node itself not intended to be exposed.
-cdef class Node:
-    cdef public:
-        double value
-        list next
-        list width
-
-
-cdef class IndexableSkiplist:
-    cdef:
-        Py_ssize_t size, maxlevels
-        Node head
-
-    cpdef get(self, Py_ssize_t i)
-    cpdef insert(self, double value)
-    cpdef remove(self, double value)

pandas/_libs/skiplist.pyx

@@ -5,144 +5,3 @@
 # Link: http://code.activestate.com/recipes/576930/
 
 # Cython version: Wes McKinney
-from random import random
-
-from libc.math cimport log
-
-import numpy as np
-
-
-# MSVC does not have log2!
-
-cdef double Log2(double x):
-    return log(x) / log(2.)
-
-
-# TODO: optimize this, make less messy
-
-cdef class Node:
-    # cdef public:
-    #    double value
-    #    list next
-    #    list width
-
-    def __init__(self, double value, list next, list width):
-        self.value = value
-        self.next = next
-        self.width = width
-
-
-# Singleton terminator node
-NIL = Node(np.inf, [], [])
-
-
-cdef class IndexableSkiplist:
-    """
-    Sorted collection supporting O(lg n) insertion, removal, and
-    lookup by rank.
-    """
-    # cdef:
-    #    Py_ssize_t size, maxlevels
-    #    Node head
-
-    def __init__(self, expected_size=100):
-        self.size = 0
-        self.maxlevels = int(1 + Log2(expected_size))
-        self.head = Node(np.NaN, [NIL] * self.maxlevels, [1] * self.maxlevels)
-
-    def __len__(self):
-        return self.size
-
-    def __getitem__(self, i):
-        return self.get(i)
-
-    cpdef get(self, Py_ssize_t i):
-        cdef:
-            Py_ssize_t level
-            Node node
-
-        node = self.head
-        i += 1
-
-        for level in range(self.maxlevels - 1, -1, -1):
-            while node.width[level] <= i:
-                i -= node.width[level]
-                node = node.next[level]
-
-        return node.value
-
-    cpdef insert(self, double value):
-        cdef:
-            Py_ssize_t level, steps, d
-            Node node, prevnode, newnode, next_at_level, tmp
-            list chain, steps_at_level
-
-        # find first node on each level where node.next[levels].value > value
-        chain = [None] * self.maxlevels
-        steps_at_level = [0] * self.maxlevels
-        node = self.head
-
-        for level in range(self.maxlevels - 1, -1, -1):
-            next_at_level = node.next[level]
-
-            while next_at_level.value <= value:
-                steps_at_level[level] = (steps_at_level[level] +
-                                         node.width[level])
-                node = next_at_level
-                next_at_level = node.next[level]
-
-            chain[level] = node
-
-        # insert a link to the newnode at each level
-        d = min(self.maxlevels, 1 - int(Log2(random())))
-        newnode = Node(value, [None] * d, [None] * d)
-        steps = 0
-
-        for level in range(d):
-            prevnode = chain[level]
-            newnode.next[level] = prevnode.next[level]
-            prevnode.next[level] = newnode
-            newnode.width[level] = (prevnode.width[level] - steps)
-            prevnode.width[level] = steps + 1
-            steps += steps_at_level[level]
-
-        for level in range(d, self.maxlevels):
-            (<Node>chain[level]).width[level] += 1
-
-        self.size += 1
-
-    cpdef remove(self, double value):
-        cdef:
-            Py_ssize_t level, d
-            Node node, prevnode, tmpnode, next_at_level
-            list chain
-
-        # find first node on each level where node.next[levels].value >= value
-        chain = [None] * self.maxlevels
-        node = self.head
-
-        for level in range(self.maxlevels - 1, -1, -1):
-            next_at_level = node.next[level]
-            while next_at_level.value < value:
-                node = next_at_level
-                next_at_level = node.next[level]
-
-            chain[level] = node
-
-        if value != (<Node>(<Node>(<Node>chain[0]).next)[0]).value:
-            raise KeyError('Not Found')
-
-        # remove one link at each level
-        d = len((<Node>(<Node>(<Node>chain[0]).next)[0]).next)
-
-        for level in range(d):
-            prevnode = chain[level]
-            tmpnode = prevnode.next[level]
-            prevnode.width[level] += tmpnode.width[level] - 1
-            prevnode.next[level] = tmpnode.next[level]
-
-        for level in range(d, self.maxlevels):
-            tmpnode = chain[level]
-            tmpnode.width[level] -= 1
-
-        self.size -= 1