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
有点晚了,但我已经做了我自己的小函数,它不环绕端点或垫与零,然后用于查找平均值。进一步的处理是,它还在线性间隔点上对信号进行重新采样。随意定制代码以获得其他特性。
该方法是一个简单的矩阵乘法与规范化高斯核。
def running_mean(y_in, x_in, N_out=101, sigma=1):
'''
Returns running mean as a Bell-curve weighted average at evenly spaced
points. Does NOT wrap signal around, or pad with zeros.
Arguments:
y_in -- y values, the values to be smoothed and re-sampled
x_in -- x values for array
Keyword arguments:
N_out -- NoOf elements in resampled array.
sigma -- 'Width' of Bell-curve in units of param x .
'''
import numpy as np
N_in = len(y_in)
# Gaussian kernel
x_out = np.linspace(np.min(x_in), np.max(x_in), N_out)
x_in_mesh, x_out_mesh = np.meshgrid(x_in, x_out)
gauss_kernel = np.exp(-np.square(x_in_mesh - x_out_mesh) / (2 * sigma**2))
# Normalize kernel, such that the sum is one along axis 1
normalization = np.tile(np.reshape(np.sum(gauss_kernel, axis=1), (N_out, 1)), (1, N_in))
gauss_kernel_normalized = gauss_kernel / normalization
# Perform running average as a linear operation
y_out = gauss_kernel_normalized @ y_in
return y_out, x_out
正弦信号加正态分布噪声的一个简单用法:
其他回答
高效的解决方案
卷积比直接的方法好得多,但(我猜)它使用FFT,因此相当慢。但是,下面的方法特别适用于计算运行平均值
def running_mean(x, N):
cumsum = numpy.cumsum(numpy.insert(x, 0, 0))
return (cumsum[N:] - cumsum[:-N]) / float(N)
要检查的代码
In[3]: x = numpy.random.random(100000)
In[4]: N = 1000
In[5]: %timeit result1 = numpy.convolve(x, numpy.ones((N,))/N, mode='valid')
10 loops, best of 3: 41.4 ms per loop
In[6]: %timeit result2 = running_mean(x, N)
1000 loops, best of 3: 1.04 ms per loop
注意numpy。allclose(result1, result2)为True,两个方法等价。 N越大,时间差异越大。
警告:虽然cumsum更快,但会增加浮点错误,这可能导致您的结果无效/不正确/不可接受
这里的评论指出了这个浮点错误问题,但我在回答中让它更明显。
# demonstrate loss of precision with only 100,000 points
np.random.seed(42)
x = np.random.randn(100000)+1e6
y1 = running_mean_convolve(x, 10)
y2 = running_mean_cumsum(x, 10)
assert np.allclose(y1, y2, rtol=1e-12, atol=0)
the more points you accumulate over the greater the floating point error (so 1e5 points is noticable, 1e6 points is more significant, more than 1e6 and you may want to resetting the accumulators) you can cheat by using np.longdouble but your floating point error still will get significant for relatively large number of points (around >1e5 but depends on your data) you can plot the error and see it increasing relatively fast the convolve solution is slower but does not have this floating point loss of precision the uniform_filter1d solution is faster than this cumsum solution AND does not have this floating point loss of precision
虽然这里有这个问题的解决方案,但请看看我的解决方案。这是非常简单和工作良好。
import numpy as np
dataset = np.asarray([1, 2, 3, 4, 5, 6, 7])
ma = list()
window = 3
for t in range(0, len(dataset)):
if t+window <= len(dataset):
indices = range(t, t+window)
ma.append(np.average(np.take(dataset, indices)))
else:
ma = np.asarray(ma)
比起numpy或scipy,我建议熊猫们更快地做到这一点:
df['data'].rolling(3).mean()
这取列“数据”的3个周期的移动平均值(MA)。你也可以计算移位的版本,例如排除当前单元格的版本(向后移位一个)可以很容易地计算为:
df['data'].shift(periods=1).rolling(3).mean()
更新:下面的例子展示了老熊猫。Rolling_mean函数,该函数在最近版本的pandas中已被删除。该函数调用的现代等价函数将使用pandas.Series.rolling:
In [8]: pd.Series(x).rolling(window=N).mean().iloc[N-1:].values
Out[8]:
array([ 0.49815397, 0.49844183, 0.49840518, ..., 0.49488191,
0.49456679, 0.49427121])
pandas比NumPy或SciPy更适合这一点。它的函数rolling_mean很方便地完成了这项工作。当输入是一个数组时,它还返回一个NumPy数组。
使用任何定制的纯Python实现都很难在性能上击败rolling_mean。下面是针对两个提议的解决方案的性能示例:
In [1]: import numpy as np
In [2]: import pandas as pd
In [3]: def running_mean(x, N):
...: cumsum = np.cumsum(np.insert(x, 0, 0))
...: return (cumsum[N:] - cumsum[:-N]) / N
...:
In [4]: x = np.random.random(100000)
In [5]: N = 1000
In [6]: %timeit np.convolve(x, np.ones((N,))/N, mode='valid')
10 loops, best of 3: 172 ms per loop
In [7]: %timeit running_mean(x, N)
100 loops, best of 3: 6.72 ms per loop
In [8]: %timeit pd.rolling_mean(x, N)[N-1:]
100 loops, best of 3: 4.74 ms per loop
In [9]: np.allclose(pd.rolling_mean(x, N)[N-1:], running_mean(x, N))
Out[9]: True
关于如何处理边缘值,也有很好的选项。
我觉得使用瓶颈可以很好地解决这个问题
参见下面的基本示例:
import numpy as np
import bottleneck as bn
a = np.random.randint(4, 1000, size=100)
mm = bn.move_mean(a, window=5, min_count=1)
“mm”是“a”的移动平均值。 “窗口”是考虑移动均值的最大条目数。 "min_count"是考虑移动平均值的最小条目数(例如,对于前几个元素或如果数组有nan值)。
好在瓶颈有助于处理nan值,而且非常高效。
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