Python中是否有SciPy函数或NumPy函数或模块来计算给定特定窗口的1D数组的运行平均值?
当前回答
对于一个简短、快速的解决方案,在一个循环中完成所有事情,没有依赖关系,下面的代码工作得很好。
mylist = [1, 2, 3, 4, 5, 6, 7]
N = 3
cumsum, moving_aves = [0], []
for i, x in enumerate(mylist, 1):
cumsum.append(cumsum[i-1] + x)
if i>=N:
moving_ave = (cumsum[i] - cumsum[i-N])/N
#can do stuff with moving_ave here
moving_aves.append(moving_ave)
其他回答
我还没有检查这有多快,但你可以试试:
from collections import deque
cache = deque() # keep track of seen values
n = 10 # window size
A = xrange(100) # some dummy iterable
cum_sum = 0 # initialize cumulative sum
for t, val in enumerate(A, 1):
cache.append(val)
cum_sum += val
if t < n:
avg = cum_sum / float(t)
else: # if window is saturated,
cum_sum -= cache.popleft() # subtract oldest value
avg = cum_sum / float(n)
有关现成的解决方案,请参见https://scipy-cookbook.readthedocs.io/items/SignalSmooth.html。 它提供了平窗类型的运行平均值。请注意,这比简单的do-it-yourself卷积方法要复杂一些,因为它试图通过反射数据来处理数据开头和结尾的问题(在您的情况下可能有效,也可能无效……)。
首先,你可以试着:
a = np.random.random(100)
plt.plot(a)
b = smooth(a, window='flat')
plt.plot(b)
更新:已经提出了更有效的解决方案,scipy的uniform_filter1d可能是“标准”第三方库中最好的,还有一些更新的或专门的库可用。
你可以用np。卷积得到:
np.convolve(x, np.ones(N)/N, mode='valid')
解释
The running mean is a case of the mathematical operation of convolution. For the running mean, you slide a window along the input and compute the mean of the window's contents. For discrete 1D signals, convolution is the same thing, except instead of the mean you compute an arbitrary linear combination, i.e., multiply each element by a corresponding coefficient and add up the results. Those coefficients, one for each position in the window, are sometimes called the convolution kernel. The arithmetic mean of N values is (x_1 + x_2 + ... + x_N) / N, so the corresponding kernel is (1/N, 1/N, ..., 1/N), and that's exactly what we get by using np.ones(N)/N.
边缘
np的模态参数。Convolve指定如何处理边缘。我在这里选择有效模式,因为我认为这是大多数人期望的运行方式,但您可能有其他优先级。下面是一个图表,说明了模式之间的差异:
import numpy as np
import matplotlib.pyplot as plt
modes = ['full', 'same', 'valid']
for m in modes:
plt.plot(np.convolve(np.ones(200), np.ones(50)/50, mode=m));
plt.axis([-10, 251, -.1, 1.1]);
plt.legend(modes, loc='lower center');
plt.show()
你可以使用scipy. nmage .uniform_filter1d:
import numpy as np
from scipy.ndimage import uniform_filter1d
N = 1000
x = np.random.random(100000)
y = uniform_filter1d(x, size=N)
uniform_filter1d:
给出具有相同numpy形状的输出(即点数) 允许多种方式处理边界,其中'reflect'是默认的,但在我的情况下,我更想要'nearest'
它也相当快(比np快近50倍)。卷积,比上述cumsum方法快2-5倍):
%timeit y1 = np.convolve(x, np.ones((N,))/N, mode='same')
100 loops, best of 3: 9.28 ms per loop
%timeit y2 = uniform_filter1d(x, size=N)
10000 loops, best of 3: 191 µs per loop
这里有3个函数可以让你比较不同实现的错误/速度:
from __future__ import division
import numpy as np
import scipy.ndimage as ndi
def running_mean_convolve(x, N):
return np.convolve(x, np.ones(N) / float(N), 'valid')
def running_mean_cumsum(x, N):
cumsum = np.cumsum(np.insert(x, 0, 0))
return (cumsum[N:] - cumsum[:-N]) / float(N)
def running_mean_uniform_filter1d(x, N):
return ndi.uniform_filter1d(x, N, mode='constant', origin=-(N//2))[:-(N-1)]
仅使用Python标准库(内存高效)
只提供标准库deque的另一个版本。令我惊讶的是,大多数答案都使用pandas或numpy。
def moving_average(iterable, n=3):
d = deque(maxlen=n)
for i in iterable:
d.append(i)
if len(d) == n:
yield sum(d)/n
r = moving_average([40, 30, 50, 46, 39, 44])
assert list(r) == [40.0, 42.0, 45.0, 43.0]
实际上,我在python文档中找到了另一个实现
def moving_average(iterable, n=3):
# moving_average([40, 30, 50, 46, 39, 44]) --> 40.0 42.0 45.0 43.0
# http://en.wikipedia.org/wiki/Moving_average
it = iter(iterable)
d = deque(itertools.islice(it, n-1))
d.appendleft(0)
s = sum(d)
for elem in it:
s += elem - d.popleft()
d.append(elem)
yield s / n
然而,在我看来,实现似乎比它应该的要复杂一些。但它肯定在标准python文档中是有原因的,有人能评论一下我的实现和标准文档吗?
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