Median of arbitrary datapoint around index - MATLAB

问题

I've been using the findpeaks function with great success to detect peaks in my signal. My next step is to clean these identified peaks, for which I have the indices.

My goal is to calculate the median of Y data points before and Y data points after a given index and replace whatever values (noise) there are with these new values (the calculated median).

Something like this:

%  points before, peak, points after
%        ↓         ↓         ↓
x = [1, 2, 3, 1,   34,   3, 2, 1, 3]

Calculate the median of the 4 data points preceding and following my peak the peak of 34...

Median of [1,2,3,1,3,2,1,3] is 2.

Replace my peak with this new value:

% Replaced peak with surrounding median
%                  ↓
x1 = [1, 2, 3, 1,  2,  3, 2, 1, 3]

Any suggestion on how to implement this?

回答1:

Find the peaks and replace them with the results of medfilt1()

[~,idx]=findpeaks(x);
if ~isempty(idx)
    m = medfilt1(x,9);
    x(idx) = m(idx);
end

回答2:

I think it is most efficient to process each peak individually. I'll demonstrate in a step-by-step manner in the following.

Take the neighborhood of each peak

x(idx_max-N:idx_max+N)

with N the number of elements to the left and right of the peak, respectively. The median of the neighborhood around each peak can be computed by using MATLAB's median() function:

median(x(idx_max-N:idx_max+N))

Now, you can replace either only the element at the peak position with the median of the neighborhood:

x(idx_max) = median(x(idx_max-N:idx_max+N))

or easily replace all elements of the neighborhood with the median value:

x(idx_max-N:idx_max+N) = median(x(idx_max-N:idx_max+N))

(Note that scalar expansion is used in the last example to assign a scalar value to multiple elements of an array.)

来源：https://stackoverflow.com/questions/47368216/median-of-arbitrary-datapoint-around-index-matlab