Get the chunks of data points on curve about a pivot value.

get_curve_chunks.py

import numpy as np
import matplotlib.pyplot as plt
import os
from scipy import integrate

CFD = os.path.dirname(__file__)


def get_chunks(x: np.ndarray[float], y: np.ndarray[float], pivot: float = 0.0):
	sort_indices = np.argsort(x)
	x, y = x[sort_indices], y[sort_indices]
	num_points = x.size
	#
	chunk_counter = 1
	previous_chunk_sign = np.sign(y[0]-pivot)
	chunks = {}
	for (i, ay) in enumerate(y):
		ay_sign = np.sign(ay-pivot)
		if ay_sign != 0.0:
			if ay_sign != previous_chunk_sign:
				chunk_counter += 1
				previous_chunk_sign = ay_sign
			#
			if chunk_counter in chunks.keys():
				chunks[chunk_counter].append([x[i], ay])
			else:
				chunks[chunk_counter] = [[x[i], ay]]
		#
	chunks = {k: np.array(v) for (k, v) in chunks.items()}
	return chunks


pvt = 5.0
X = np.linspace(0.0*np.pi, 1.5*np.pi, 2000)
Y = np.sin(X) + pvt

CHUNKS = get_chunks(X, Y, pivot=pvt)

# evaluate areas
areas = {k: integrate.simpson(v[:, 1]-pvt, v[:, 0]) for (k, v) in CHUNKS.items()}

plt.figure()
for (k, v) in CHUNKS.items():
	print(f"Area of chunk-{k} is {areas[k]:4.3f}")
	plt.plot(v[:, 0], v[:, 1], label=f'chunk-{k}')
plt.legend(loc='best')
plt.savefig(os.path.join(CFD, "sinx.png"))
plt.close()