Peak detection in Python [Eli Billauer]

readme.md

I just directly translated to Python from this MATLAB script, which I've also included here. The original is public domain, so my translation is, too.

Also see Frequency estimation methods in Python for interpolating to get sharp intersample peaks

sixtenbe has posted a more powerful version here

and there's a PyPI repo

peakdet.m

function [maxtab, mintab]=peakdet(v, delta, x)
%PEAKDET Detect peaks in a vector
%        [MAXTAB, MINTAB] = PEAKDET(V, DELTA) finds the local
%        maxima and minima ("peaks") in the vector V.
%        MAXTAB and MINTAB consists of two columns. Column 1
%        contains indices in V, and column 2 the found values.
%      
%        With [MAXTAB, MINTAB] = PEAKDET(V, DELTA, X) the indices
%        in MAXTAB and MINTAB are replaced with the corresponding
%        X-values.
%
%        A point is considered a maximum peak if it has the maximal
%        value, and was preceded (to the left) by a value lower by
%        DELTA.

% Eli Billauer, 3.4.05 (Explicitly not copyrighted).
% This function is released to the public domain; Any use is allowed.

maxtab = [];
mintab = [];

v = v(:); % Just in case this wasn't a proper vector

if nargin < 3
  x = (1:length(v))';
else 
  x = x(:);
  if length(v)~= length(x)
    error('Input vectors v and x must have same length');
  end
end
  
if (length(delta(:)))>1
  error('Input argument DELTA must be a scalar');
end

if delta <= 0
  error('Input argument DELTA must be positive');
end

mn = Inf; mx = -Inf;
mnpos = NaN; mxpos = NaN;

lookformax = 1;

for i=1:length(v)
  this = v(i);
  if this > mx, mx = this; mxpos = x(i); end
  if this < mn, mn = this; mnpos = x(i); end
  
  if lookformax
    if this < mx-delta
      maxtab = [maxtab ; mxpos mx];
      mn = this; mnpos = x(i);
      lookformax = 0;
    end  
  else
    if this > mn+delta
      mintab = [mintab ; mnpos mn];
      mx = this; mxpos = x(i);
      lookformax = 1;
    end
  end
end

peakdetect.py

import sys
from numpy import NaN, Inf, arange, isscalar, asarray, array

def peakdet(v, delta, x = None):
    """
    Converted from MATLAB script at http://billauer.co.il/peakdet.html
    
    Returns two arrays
    
    function [maxtab, mintab]=peakdet(v, delta, x)
    %PEAKDET Detect peaks in a vector
    %        [MAXTAB, MINTAB] = PEAKDET(V, DELTA) finds the local
    %        maxima and minima ("peaks") in the vector V.
    %        MAXTAB and MINTAB consists of two columns. Column 1
    %        contains indices in V, and column 2 the found values.
    %      
    %        With [MAXTAB, MINTAB] = PEAKDET(V, DELTA, X) the indices
    %        in MAXTAB and MINTAB are replaced with the corresponding
    %        X-values.
    %
    %        A point is considered a maximum peak if it has the maximal
    %        value, and was preceded (to the left) by a value lower by
    %        DELTA.
    
    % Eli Billauer, 3.4.05 (Explicitly not copyrighted).
    % This function is released to the public domain; Any use is allowed.
    
    """
    maxtab = []
    mintab = []
       
    if x is None:
        x = arange(len(v))
    
    v = asarray(v)
    
    if len(v) != len(x):
        sys.exit('Input vectors v and x must have same length')
    
    if not isscalar(delta):
        sys.exit('Input argument delta must be a scalar')
    
    if delta <= 0:
        sys.exit('Input argument delta must be positive')
    
    mn, mx = Inf, -Inf
    mnpos, mxpos = NaN, NaN
    
    lookformax = True
    
    for i in arange(len(v)):
        this = v[i]
        if this > mx:
            mx = this
            mxpos = x[i]
        if this < mn:
            mn = this
            mnpos = x[i]
        
        if lookformax:
            if this < mx-delta:
                maxtab.append((mxpos, mx))
                mn = this
                mnpos = x[i]
                lookformax = False
        else:
            if this > mn+delta:
                mintab.append((mnpos, mn))
                mx = this
                mxpos = x[i]
                lookformax = True

    return array(maxtab), array(mintab)

if __name__=="__main__":
    from matplotlib.pyplot import plot, scatter, show
    series = [0,0,0,2,0,0,0,-2,0,0,0,2,0,0,0,-2,0]
    maxtab, mintab = peakdet(series,.3)
    plot(series)
    scatter(array(maxtab)[:,0], array(maxtab)[:,1], color='blue')
    scatter(array(mintab)[:,0], array(mintab)[:,1], color='red')
    show()

Thanks man!

Thanks for sharing your code! It works very well for my project.