CODEWITHSUNDEEP
pythonlisttuplespython-3.6
Gary
Gary

Reputation: 57

Comparing a tuple of a pair to a list of tuple pairs

So I am working on this programming homework and I am currently stuck on comparing the pairs of values in one tuple to the tuple pairs in a list.

The pairs are basically x and y coordinates and I need to find the closest one from the list to the tuple pair. As an example, given the point (-4, 3) and the list [(10, 6), (1, 7), (6, 3), (1, 9)], the closest one would be (1, 7).

These numbers always changes with a randoming part of the programming but the the above is defined as a function. Here is the whole thing:

def nearest(point, more_points):
    '''
    Finds the nearest point to the base point
    '''
    (x, y) = point
    for i, j in more_points:
        a = math.fabs(x - i)
        tempI = i
        b = math.fabs(y - j)
        tempJ = j
        tempA, tempB = a , b
        if min(tempA) <  a:

point = () 
my_points = []
c = 0
lpoint = list(point)
while c < 2:
     lpoint.append(random.randrange(-5,5,1)) # generate the "point"
     c += 1
tpoint = tuple(lpoint)
c = 0
colx = [] # x points
coly = [] # y points
# generate the points
while c < 4:
    colx.append(random.randint(0,10))
    coly.append(random.randint(0,10))
    c += 1

my_point = list(zip(colx,coly))
print(my_point)
the_nearest = nearest(tpoint,my_point)
print(the_nearest)

What I am trying to do is to take the x,y in the point and then take the "other" point and get the difference and then use that to find the "nearest" but I lost and I am stuck. The focus is on the user defined function.

Upvotes: 1

Views: 793

Answers (2)

Harvey
Harvey

Reputation: 5821

Use min() with a key function:

#!/usr/bin/env python3

import math
from functools import partial


def distance_between_points(a, b):
    ax, ay = a
    bx, by = b
    return math.sqrt(pow(ax - bx, 2) + pow(ay - by, 2))


def nearest(point, more_points):
    '''
    Finds the nearest point to the base point
    '''
    distance_to_point = partial(distance_between_points, point)
    return min(more_points, key=distance_to_point)


point = (-4, 3)
my_points = [(10, 6), (1, 7), (6, 3), (1, 9)]
n = nearest(point, my_points)
print(n)

Upvotes: 0

FunkySayu
FunkySayu

Reputation: 8061

Assuming the following function calculate the distance within 2 points:

def distance(point_a, point_b):
    """Returns the distance between two points."""
    x0, y0 = point_a
    x1, y1 = point_b
    return math.fabs(x0 - x1) + math.fabs(y0 - y1)

You can iterate over all points and find the minimum distance:

def nearest(point, all_points):
    closest_point, best_distance = None, float("inf")
    for other_point in all_points:
        d = distance(point, other_point)
        if d < best_distance:
             closest_point, best_distance = other_point, d
    return closest_point

Although I could come up with a more pythonic approach:

def nearest(point, all_points):
    """Returns the closest point in all_points from the first parameter."""
    distance_from_point = functools.partial(distance, point)
    return min(all_points, key=distance_from_point)

The overall idea of the above solution is to build a partial function. This partial function takes a single parameter and returns the distance to the point given as parameter. This is could be re-written as lambda other_point: distance(point, other_point) but this is prettier.

Note the above function will raise ValueError if you call it with an empty list of points: nearest(point, []). You can add an if for this case if necessary.

Upvotes: 5

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