Finding several regions of interest in an array

问题

Say I have conducted an experiment where I've left a python program running for some long time and in that time I've taken several measurements of some quantity against time. Each measurement is separated by some value between 1 and 3 seconds with the time step used much smaller than that... say 0.01s. An example of such an even if you just take the y axis might look like:

[...0,1,-1,4,1,0,0,2,3,1,0,-1,2,3,5,7,8,17,21,8,3,1,0,0,-2,-17,-20,-10,-3,3,1,0,-2,-1,1,0,0,1,-1,0,0,2,0...]

Here we have some period of inactivity followed by a sharp rise, fall, a brief pause around 0, drop sharply, rise sharply and settle again around 0. The dots indicate that this is part of a long stream of data extending in both directions. There will be many of these events over the whole dataset with varying lengths separated by low magnitude regions.

I wish to essentially form an array of 'n' arrays (tuples?) with varying lengths capturing just the events so I can analyse them separately later. I can't separate purely by an np.absolute() type threshold because there are occasional small regions of near zero values within a given event such as in the above example. In addition to this there may be occasional blips in between measurements with large magnitudes but short duration.

The sample above would ideally end up as with a couple of elements or so from the flat region either side or so.

[0,-1,2,3,5,7,8,17,21,8,3,1,0,0,-2,-17,-20,-10,-3,3,1,0,-2,-1]

I'm thinking something like:

Input:

[0,1,0,0,-1,4,8,22,16,7,2,1,0,-1,-17,-20,-6,-1,0,1,0,2,1,0,8,-7,-1,0,0,1,0,1,-1,-17,-22,-40,16,1,3,14,17,19,8,2,0,1,3,2,3,1,0,0,-2,1,0,0,-1,22,4,0,-1,0]

Split based on some number of consecutive values below a magnitude of 2.

[[-1,4,8,22,16,7,2,1,0,-1,-17,-20,-6,-1],[8,-7,-1,0],[-1,-17,-22,-40,16,1,3,14,17,19,8,2,0],[1,22,4,]]

Like in this graph:

If sub arrays length is less than say 10 then remove:

[[-1,4,8,22,16,7,2,1,0,-1,-17,-20,-6,-1],[-1,-17,-22,-40,16,1,3,14,17,19,8,2,0]]

Is this a good way to approach it? The first step is confusing me a little also. I need to preserve those small low magnitude regions within an event also.

Re-edited! I'm going to be comparing two signals each measured as a function of time so they will be zipped together in a list of tuples.

回答1:

Here is my two cents, based on exponential smoothing.

import itertools
A=np.array([0,1,0,0,-1,4,8,22,16,7,2,1,0,-1,-17,-20,-6,-1,0,1,0,2,1,0,8,-7,-1,0,0,1,0,1,-1,-17,-22,-40,16,1,3,14,17,19,8,2,0,1,3,2,3,1,0,0,-2,1,0,0,-1,22,4,0,-1,0])
B=np.hstack(([0,0],A,[0,0]))
B=np.asanyarray(zip(*[B[i:] for i in range(5)]))
C=(B*[0.25,0.5,1,0.5,0.25]).mean(axis=1) #C is the 5-element sliding windows exponentially smoothed signal
D=[]
for item in itertools.groupby(enumerate(C), lambda x: abs(x[1])>1.5): 
    if item[0]:
        D.append(list(item[1])) #Get the indices where the signal are of magnitude >2. Change 1.5 to control the behavior.
E=[D[0]]
for item in D[1:]:
    if (item[0][0]-E[-1][-1][0]) <5: #Merge interesting regions if they are 5 or less indices apart. Change 5 to control the behavior.
        E[-1]=E[-1]+item
    else:
        E.append(item)
print [(item[0][0], item[-1][0]) for item in E]
[A[item[0][0]: item[-1][0]] for item in E if (item[-1][0]-item[0][0])>9] #Filter out the interesting regions <10 in length.

来源：https://stackoverflow.com/questions/22441259/finding-several-regions-of-interest-in-an-array