Revert "BLD: remove blockslider pandas-dev#34014"

This reverts commit 687a0ce.

Author: fangchenli

pandas/_libs/reduction.pyx

@@ -1,20 +1,24 @@
 from copy import copy
 
+from cython import Py_ssize_t
+
+from libc.stdlib cimport free, malloc
+
 import numpy as np
 
 cimport numpy as cnp
 from numpy cimport int64_t, ndarray
 
 cnp.import_array()
 
-from pandas._libs.util cimport is_array
+from pandas._libs cimport util
 
 from pandas._libs.lib import is_scalar, maybe_convert_objects
 
 
 cpdef check_result_array(object obj, Py_ssize_t cnt):
 
-    if (is_array(obj) or
+    if (util.is_array(obj) or
             (isinstance(obj, list) and len(obj) == cnt) or
             getattr(obj, 'shape', None) == (cnt,)):
         raise ValueError('Must produce aggregated value')
@@ -29,7 +33,7 @@ cdef class _BaseGrouper:
         if (dummy.dtype != self.arr.dtype
                 and values.dtype != self.arr.dtype):
             raise ValueError('Dummy array must be same dtype')
-        if is_array(values) and not values.flags.contiguous:
+        if util.is_array(values) and not values.flags.contiguous:
             # e.g. Categorical has no `flags` attribute
             values = values.copy()
         index = dummy.index.values
@@ -102,7 +106,7 @@ cdef class SeriesBinGrouper(_BaseGrouper):
         self.f = f
 
         values = series.values
-        if is_array(values) and not values.flags.c_contiguous:
+        if util.is_array(values) and not values.flags.c_contiguous:
             # e.g. Categorical has no `flags` attribute
             values = values.copy('C')
         self.arr = values
@@ -200,7 +204,7 @@ cdef class SeriesGrouper(_BaseGrouper):
         self.f = f
 
         values = series.values
-        if is_array(values) and not values.flags.c_contiguous:
+        if util.is_array(values) and not values.flags.c_contiguous:
             # e.g. Categorical has no `flags` attribute
             values = values.copy('C')
         self.arr = values
@@ -284,9 +288,9 @@ cpdef inline extract_result(object res, bint squeeze=True):
         res = res._values
         if squeeze and res.ndim == 1 and len(res) == 1:
             res = res[0]
-    if hasattr(res, 'values') and is_array(res.values):
+    if hasattr(res, 'values') and util.is_array(res.values):
         res = res.values
-    if is_array(res):
+    if util.is_array(res):
         if res.ndim == 0:
             res = res.item()
         elif squeeze and res.ndim == 1 and len(res) == 1:
@@ -300,7 +304,7 @@ cdef class Slider:
     """
     cdef:
         ndarray values, buf
-        Py_ssize_t stride, orig_len
+        Py_ssize_t stride, orig_len, orig_stride
         char *orig_data
 
     def __init__(self, ndarray values, ndarray buf):
@@ -316,6 +320,7 @@ cdef class Slider:
 
         self.orig_data = self.buf.data
         self.orig_len = self.buf.shape[0]
+        self.orig_stride = self.buf.strides[0]
 
         self.buf.data = self.values.data
         self.buf.strides[0] = self.stride
@@ -329,8 +334,9 @@ cdef class Slider:
 
     cdef reset(self):
 
-        self.buf.data = self.orig_data
         self.buf.shape[0] = self.orig_len
+        self.buf.data = self.orig_data
+        self.buf.strides[0] = self.orig_stride
 
 
 class InvalidApply(Exception):
@@ -340,6 +346,7 @@ class InvalidApply(Exception):
 def apply_frame_axis0(object frame, object f, object names,
                       const int64_t[:] starts, const int64_t[:] ends):
     cdef:
+        BlockSlider slider
         Py_ssize_t i, n = len(starts)
         list results
         object piece
@@ -350,13 +357,16 @@ def apply_frame_axis0(object frame, object f, object names,
 
     results = []
 
+    slider = BlockSlider(frame)
+
     mutated = False
-    item_cache = frame._item_cache
+    item_cache = slider.dummy._item_cache
     try:
         for i in range(n):
+            slider.move(starts[i], ends[i])
 
             item_cache.clear()  # ugh
-            chunk = frame[starts[i]:ends[i]]
+            chunk = slider.dummy
             object.__setattr__(chunk, 'name', names[i])
 
             try:
@@ -389,6 +399,82 @@ def apply_frame_axis0(object frame, object f, object names,
             if require_slow_apply:
                 break
     finally:
-        pass
+        slider.reset()
 
     return results, mutated
+
+
+cdef class BlockSlider:
+    """
+    Only capable of sliding on axis=0
+    """
+
+    cdef public:
+        object frame, dummy, index
+        int nblocks
+        Slider idx_slider
+        list blocks
+
+    cdef:
+        char **base_ptrs
+
+    def __init__(self, object frame):
+        cdef:
+            Py_ssize_t i
+            object b
+
+        self.frame = frame
+        self.dummy = frame[:0]
+        self.index = self.dummy.index
+
+        self.blocks = [b.values for b in self.dummy._mgr.blocks]
+
+        for x in self.blocks:
+            util.set_array_not_contiguous(x)
+
+        self.nblocks = len(self.blocks)
+        # See the comment in indexes/base.py about _index_data.
+        # We need this for EA-backed indexes that have a reference to a 1-d
+        # ndarray like datetime / timedelta / period.
+        self.idx_slider = Slider(
+            self.frame.index._index_data, self.dummy.index._index_data)
+
+        self.base_ptrs = <char**>malloc(sizeof(char*) * len(self.blocks))
+        for i, block in enumerate(self.blocks):
+            self.base_ptrs[i] = (<ndarray>block).data
+
+    def __dealloc__(self):
+        free(self.base_ptrs)
+
+    cdef move(self, int start, int end):
+        cdef:
+            ndarray arr
+            Py_ssize_t i
+
+        # move blocks
+        for i in range(self.nblocks):
+            arr = self.blocks[i]
+
+            # axis=1 is the frame's axis=0
+            arr.data = self.base_ptrs[i] + arr.strides[1] * start
+            arr.shape[1] = end - start
+
+        # move and set the index
+        self.idx_slider.move(start, end)
+
+        object.__setattr__(self.index, '_index_data', self.idx_slider.buf)
+        self.index._engine.clear_mapping()
+        self.index._cache.clear()  # e.g. inferred_freq must go
+
+    cdef reset(self):
+        cdef:
+            ndarray arr
+            Py_ssize_t i
+
+        # reset blocks
+        for i in range(self.nblocks):
+            arr = self.blocks[i]
+
+            # axis=1 is the frame's axis=0
+            arr.data = self.base_ptrs[i]
+            arr.shape[1] = 0