如何在numpy.ndarray上滾動（window = 3）.max（）？

Question

我有一個numpy.ndarray如下。 它是talib.RSI的輸出。 這是numpy.ndarray的類型。 我想獲取滾動（windows = 3）.max（）和滾動（window = 3）.min的列表

怎么做？

[         nan          nan          nan          nan          nan
          nan          nan          nan          nan          nan
          nan          nan          nan          nan  56.50118203
  60.05461743  56.99068148  55.70899949  59.2299361   64.19044898
  60.62186599  53.96346826  44.06538636  52.04519976  51.32884016
  58.65240379  60.44789401  58.94743634  59.75308787  53.56534397
  54.22091468  47.22502341  51.5425848   50.0923126   49.80608264
  45.69087847  50.07778871  54.21701441  58.79268406  63.59307774
  66.08195696  65.49255218  65.11035657  68.47403716  70.70530564
  73.21955929  76.57474822  65.89852612  66.51497688  72.42658468
  73.80944844  69.56561001]

Answer 1

如果您負擔得起添加新的依賴項，那么我寧願使用Pandas做到這一點。

import numpy
import pandas


x = numpy.array([0, 1, 2, 3, 4])
s = pandas.Series(x)

print(s.rolling(3).min())
print(s.rolling(3).max())
print(s.rolling(3).mean())
print(s.rolling(3).std())

請注意，將NumPy數組轉換為Pandas系列不會創建該數組的副本，因為Pandas在內部將NumPy數組用於其系列。

Answer 2

您可以使用np.lib.stride_tricks.as_strided ：

# a smaller example
import numpy.random as npr
npr.seed(123)
arr = npr.randn(10)
arr[:4] = np.nan    

windows = np.lib.stride_tricks.as_strided(arr, shape=(8, 3), strides=(8, 8))

print(windows.max(axis=1))
print(windows.sum(axis=1))
[        nan         nan         nan         nan  1.65143654  1.65143654
  1.26593626  1.26593626]
[        nan         nan         nan         nan -1.35384296 -1.20415534
 -1.58965561 -0.02971677]