CODEWITHSUNDEEP
python
barciewicz
barciewicz

Reputation: 3813

Pass result from one "for" loop iteration to next iteration?

I have a list of latitude/longitude coordinates and I want to create a line from them:

import time
import random

class Point:
    def __init__(self, lng, lat, neighbours):
        self.x = lng
        self.y = lat
        self.neighbours = neighbours

def find_neighbours(point):
        '''Simulate neighbour search in kdtree'''
        print(f'Searching for {point} in the tree')
        time.sleep(1)
        neighbours = random.randint(0, 100)
        return neighbours

class Line:
    def __init__(self, point_A, point_B):
        self.point_A = point_A
        self.point_B = point_B
        self.line = [
            point_A, 
            point_B,
        ]

def get_points():
    return [
    [51.11453, 17.10942],
    [51.11441, 17.10941],
    [51.11349, 17.10779],
    [51.11367, 17.10733],
    [51.1143, 17.10648],
    [51.11493, 17.10553],
    [51.11471, 17.10519],
    [51.11434, 17.10506],
    [51.11376, 17.10462],
    [51.11372, 17.10433],
    [51.11353, 17.1042],
    [51.11388, 17.10168],
    [51.11386, 17.10108],
    [51.11362, 17.10098],
    [51.11177, 17.10099],
    [51.11169, 17.10105],
    [51.11169, 17.10129],
]

def make_lines_from_points(points):
    lines = []

    for index, point in enumerate(points):
        try:
            next_point = points[index + 1]
        except IndexError: 
            # last point reached, so no need to make a line
            next_point = None

        if next_point:
            point_A = Point(
                point[1],
                point[0],
                find_neighbours(point)
            )
            point_B = Point(
                next_point[1],
                next_point[0],
                find_neighbours(next_point)
            )
            line = Line(point_A, point_B)
            lines.append(line.line)
    return lines

def main():
    points = get_points()
    lines = make_lines_from_points(points)
    print(lines)

if __name__ == '__main__':
    main()

In this code, I am turning every coordinate and the coordinate next to it into instances of Point class, and then create and instance of Line from such two points.

Upon initialization of each Point instance, point's neighbours have to be found and assigned to instance's neighbours attribute. This will potentially take a longer time.

With that in mind, I want to improve the for loop so that point B becomes point A in the next iteration, in order to avoid computing the neighbours again for the same point.

How can I do that?

Upvotes: 1

Views: 80

Answers (2)

Kai Winkler
Kai Winkler

Reputation: 89

def make_lines_from_points(points):
    lines = []

    point_A = None

    for index, point in enumerate(points):
        try:
            next_point = points[index + 1]
        except IndexError: 
            # last point reached, so no need to make a line
            next_point = None

        if next_point:
            if not point_A:
                point_A = Point(
                    point[1],
                    point[0],
                    find_neighbours(point)
                )
            point_B = Point(
                next_point[1],
                next_point[0],
                find_neighbours(next_point)
            )

            point_A = point_B

            line = Line(point_A, point_B)
            lines.append(line.line)
    return lines

Upvotes: 0

lenik
lenik

Reputation: 23556

You may try this:

def make_lines_from_points(points):
    lines = []

    saved_neighbours = None
    for index, point in enumerate(points):
        try:
            next_point = points[index + 1]
        except IndexError: 
            # last point reached, so no need to make a line
            next_point = None

        if next_point:
            point_A = Point(
                point[1],
                point[0],
                saved_neighbours if saved_neighbours is not None else find_neighbours(point)
            )
            point_B = Point(
                next_point[1],
                next_point[0],
                find_neighbours(next_point)
            )
            line = Line(point_A, point_B)
            lines.append(line.line)
            saved_neighbours = point_B.neighbours
    return lines

Upvotes: 1

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