Find value close to number in python array and index it

Question

This is the code I have so far:

import numpy as np

#make amplitude and sample arrays
amplitude=[0,1,2,3, 5.5, 6,5,2,2, 4, 2,3,1,6.5,5,7,1,2,2,3,8,4,9,2,3,4,8,4,9,3]
#print(amplitude)

#split arrays up into a line for each sample
traceno=5                  #number of traces in file
samplesno=6                #number of samples in each trace. This wont change.

amplitude_split=np.array(amplitude, dtype=np.int).reshape((traceno,samplesno))
print(amplitude_split)

#find max value of trace
max_amp=np.amax(amplitude_split,1)
print(max_amp)

#find index of max value
ind_max_amp=np.argmax(amplitude_split, axis=1, out=None)
#print(ind_max_amp)

#find 90% of max value of trace
amp_90=np.amax(amplitude_split,1)*0.9
print(amp_90)

I would like to find the value in each line of the array that is closest to the corresponding amp_90. I would also like to be able to obtain the index of this number. Please help!

n.b. I know this is easy to do by eye, but it is a test data set before I apply it to my real data!

By closest you mean in absolute terms? What is the expected output? — Dani Mesejo
– Dani Mesejo, Commented Apr 15, 2020 at 16:29
Yep. Just to note that in my "real" data I wont be dealing with just integers... not sure if this matters or not — okvoyce
– okvoyce, Commented Apr 15, 2020 at 16:32

Dani Mesejo · Accepted Answer · 2020-04-15 16:32:15Z

1

IIUC, you could do the following:

# find the indices of the min absolute difference 
indices = np.argmin(np.abs(amplitude_split - amp_90[:, None]), axis=1)

# get the values at those positions
result = amplitude_split[np.arange(5), indices]

print(result)

answered Apr 15, 2020 at 16:32

Dani Mesejo

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