# Python: How to get local maxima values from 1D-array or list

I am pretty new in Python and I have a problem which I could not solve with found answers… hopefully someone can help:
I need to get a list of all local maxima of a data-set which is imported from a csv-file.
Values range from 0 to 0.5 or so.

I just need to get a list of those local maxima of one data row (“Werte”, array or “N”, list) to do statistics on them.

This is what I have got:

``````import numpy as np
from numpy import *

N = []

file = open('C:/Auswertung/PEE/PEE_L_1_O_130702-1.1.csv', 'r')
Probe = file.readline()         # lese Inhalt zeilenweise in Listen

for row in data:
columns = row.split(";")       # Trenne Zeilen bei ';'
N.append(float(columns))

Werte = np.array([N])

# one try here: only gives me a set of 1s...
c = (diff(sign(diff(Werte))) < 0).nonzero() + 1 # local max
print(c)
``````

is there anyone who could help me find the right way to do it?
Thank you a lot!

I think you are looking for `argrelmax`, from `scipy.signal`. It gives you the indices of the relative maxima of a 1d array.

``````from scipy.signal import argrelmax
t=linspace(-4,40,1000)
y=sin(t)
argrelmax(y)
``````

with result

``````[126 269 412 554 697 840 982]
``````

to get the values, use

``````y[argrelmax(y)]
``````

EDIT:

notice that it does not count local maxima at the extreme of your domain.