Performance increase rolling min max (pandas-dev#19549)

Author: hexgnu

asv_bench/benchmarks/rolling.py

@@ -16,12 +16,26 @@ class Methods(object):
 
     def setup(self, constructor, window, dtype, method):
         N = 10**5
-        arr = np.random.random(N).astype(dtype)
+        arr = (100 * np.random.random(N)).astype(dtype)
         self.roll = getattr(pd, constructor)(arr).rolling(window)
 
     def time_rolling(self, constructor, window, dtype, method):
         getattr(self.roll, method)()
 
+class VariableWindowMethods(Methods):
+    sample_time = 0.2
+    params = (['DataFrame', 'Series'],
+              ['50s', '1h', '1d'],
+              ['int', 'float'],
+              ['median', 'mean', 'max', 'min', 'std', 'count', 'skew', 'kurt',
+               'sum'])
+    param_names = ['contructor', 'window', 'dtype', 'method']
+
+    def setup(self, constructor, window, dtype, method):
+        N = 10**5
+        arr = (100 * np.random.random(N)).astype(dtype)
+        index = pd.date_range('2017-01-01', periods=N, freq='5s')
+        self.roll = getattr(pd, constructor)(arr, index=index).rolling(window)
 
 class Pairwise(object):
 

doc/source/whatsnew/v0.23.0.txt

@@ -645,6 +645,7 @@ Performance Improvements
 - Improved performance of :func:`MultiIndex.get_loc` for large indexes, at the cost of a reduction in performance for small ones (:issue:`18519`)
 - Improved performance of pairwise ``.rolling()`` and ``.expanding()`` with ``.cov()`` and ``.corr()`` operations (:issue:`17917`)
 - Improved performance of :func:`DataFrameGroupBy.rank` (:issue:`15779`)
+- Improved performance of variable ``.rolling()`` on ``.min()`` and ``.max()`` (:issue:`19521`)
 
 .. _whatsnew_0230.docs:
 

pandas/_libs/src/headers/cmath

@@ -0,0 +1,15 @@
+#ifndef _PANDAS_MATH_H_
+#define _PANDAS_MATH_H_
+
+// In older versions of Visual Studio there wasn't a std::signbit defined
+// This defines it using _copysign
+#if defined(_MSC_VER) && (_MSC_VER < 1800)
+#include <cmath>
+namespace std {
+  __inline int signbit(double num) { return _copysign(1.0, num) < 0; }
+}
+#else
+#include <cmath>
+#endif
+
+#endif

pandas/_libs/src/headers/math.h

@@ -3,6 +3,7 @@
 
 cimport cython
 from cython cimport Py_ssize_t
+from libcpp.deque cimport deque
 
 from libc.stdlib cimport malloc, free
 
@@ -12,7 +13,7 @@ from numpy cimport ndarray, double_t, int64_t, float64_t
 cnp.import_array()
 
 
-cdef extern from "../src/headers/math.h":
+cdef extern from "../src/headers/cmath" namespace "std":
     int signbit(double) nogil
     double sqrt(double x) nogil
 
@@ -1222,8 +1223,9 @@ cdef _roll_min_max(ndarray[numeric] input, int64_t win, int64_t minp,
     cdef:
         numeric ai
         bint is_variable, should_replace
-        int64_t s, e, N, i, j, removed
+        int64_t N, i, removed, window_i
         Py_ssize_t nobs = 0
+        deque Q[int64_t]
         ndarray[int64_t] starti, endi
         ndarray[numeric, ndim=1] output
     cdef:
@@ -1242,32 +1244,48 @@ cdef _roll_min_max(ndarray[numeric] input, int64_t win, int64_t minp,
 
     output = np.empty(N, dtype=input.dtype)
 
+    Q = deque[int64_t]()
+
     if is_variable:
 
         with nogil:
 
-            for i in range(N):
-                s = starti[i]
-                e = endi[i]
+            # This is using a modified version of the C++ code in this
+            # SO post: http://bit.ly/2nOoHlY
+            # The original impl didn't deal with variable window sizes
+            # So the code was optimized for that
 
-                r = input[s]
-                nobs = 0
-                for j in range(s, e):
+            for i from starti[0] <= i < endi[0]:
+                ai = init_mm(input[i], &nobs, is_max)
 
-                    # adds, death at the i offset
-                    ai = init_mm(input[j], &nobs, is_max)
+                if is_max:
+                    while not Q.empty() and ai >= input[Q.back()]:
+                        Q.pop_back()
+                else:
+                    while not Q.empty() and ai <= input[Q.back()]:
+                        Q.pop_back()
+                Q.push_back(i)
 
-                    if is_max:
-                        if ai > r:
-                            r = ai
-                    else:
-                        if ai < r:
-                            r = ai
+            for i from endi[0] <= i < N:
+                output[i-1] = calc_mm(minp, nobs, input[Q.front()])
 
-                output[i] = calc_mm(minp, nobs, r)
+                ai = init_mm(input[i], &nobs, is_max)
 
-    else:
+                if is_max:
+                    while not Q.empty() and ai >= input[Q.back()]:
+                        Q.pop_back()
+                else:
+                    while not Q.empty() and ai <= input[Q.back()]:
+                        Q.pop_back()
 
+                while not Q.empty() and Q.front() <= i - (endi[i] - starti[i]):
+                    Q.pop_front()
+
+                Q.push_back(i)
+
+            output[N-1] = calc_mm(minp, nobs, input[Q.front()])
+
+    else:
         # setup the rings of death!
         ring = <numeric *>malloc(win * sizeof(numeric))
         death = <int64_t *>malloc(win * sizeof(int64_t))

pandas/_libs/window.pyx

@@ -617,7 +617,8 @@ def pxd(name):
         'pyxfile': '_libs/testing'},
     '_libs.window': {
         'pyxfile': '_libs/window',
-        'pxdfiles': ['_libs/skiplist', '_libs/src/util']},
+        'pxdfiles': ['_libs/skiplist', '_libs/src/util'],
+        'language': 'c++'},
     '_libs.writers': {
         'pyxfile': '_libs/writers',
         'pxdfiles': ['_libs/src/util']},
@@ -640,11 +641,11 @@ def pxd(name):
                     sources=sources,
                     depends=data.get('depends', []),
                     include_dirs=include,
+                    language=data.get('language', 'c'),
                     extra_compile_args=extra_compile_args)
 
     extensions.append(obj)
 
-
 # ----------------------------------------------------------------------
 # msgpack