Peak finding (find_peaks) in SciPy - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Find peaks in a simple signal

What is the output of the following code that finds peaks in a signal array?

SciPy

import numpy as np
from scipy.signal import find_peaks

signal = np.array([0, 2, 1, 3, 0, 1, 2, 1, 0])
peaks, _ = find_peaks(signal)
print(peaks.tolist())

A [1, 3, 5, 6]

B [0, 3, 6]

C [2, 4, 7]

D [1, 3, 6]

💡 Hint

Peaks are points higher than their immediate neighbors.

The peaks are at indices 1 (value 2), 3 (value 3), and 6 (value 2) because these points are greater than their neighbors.

❓ data_output

intermediate

Count peaks with minimum height

Given the signal array, how many peaks have a height of at least 3?

SciPy

import numpy as np
from scipy.signal import find_peaks

signal = np.array([1, 3, 7, 1, 2, 6, 0, 1])
peaks, properties = find_peaks(signal, height=3)
print(len(peaks))

A 3

B 2

C 4

D 1

💡 Hint

Check which peaks have values >= 3.

Peaks are at indices 2 (7) and 5 (6), both >= 3, so count is 2.

❓ visualization

advanced

Visualize peaks with minimum distance

Which plot correctly shows peaks found with a minimum distance of 3 between them?

SciPy

import numpy as np
import matplotlib.pyplot as plt
from scipy.signal import find_peaks

signal = np.array([0, 2, 1, 3, 0, 1, 2, 1, 0])
peaks, _ = find_peaks(signal, distance=3)
plt.plot(signal)
plt.plot(peaks, signal[peaks], "x")
plt.show()

A Plot with peaks marked at indices 0, 3, and 6

B Plot with peaks marked at indices 1, 3, and 6

C Plot with peaks marked at indices 1 and 6 only

D Plot with peaks marked at indices 3 and 6 only

💡 Hint

Minimum distance means peaks must be at least 3 indices apart.

Peaks at indices 1 and 6 are at least 3 apart. Peak at 3 is too close to 1, so it is excluded.

🔧 Debug

advanced

Identify error in peak finding code

What error does the following code produce?

SciPy

import numpy as np
from scipy.signal import find_peaks

signal = [1, 2, 3, 2, 1]
peaks, properties = find_peaks(signal, height='high')

A ValueError: height must be a number or tuple of numbers

B No error, returns peaks at indices [2]

C SyntaxError: invalid syntax

D TypeError: '>' not supported between instances of 'str' and 'int'

💡 Hint

Check the type of the height parameter.

The height parameter expects a number or tuple, but a string 'high' is given, causing a ValueError.

🚀 Application

expert

Find peaks with multiple conditions

Which option correctly finds peaks in the signal that have a height of at least 2 and a prominence of at least 1?

SciPy

import numpy as np
from scipy.signal import find_peaks

signal = np.array([0, 2, 1, 3, 0, 1, 2, 1, 0])
peaks, properties = find_peaks(signal, height=2, prominence=1)
print(peaks.tolist())

A [3, 6]

B [1, 3]

C [1, 3, 6]

D [1, 6]

💡 Hint

Prominence measures how much a peak stands out from its surroundings.

Peaks at indices 3 and 6 meet both height >= 2 and prominence >= 1 conditions.