Finding closest pair of coordinates from a list

Question

I am attempting to implement the solution to a previous SO question

I have a pair of coordinates that I wish to find the closest associated pair of coordinates in a list of coordinates.

This can be achieved by finding the pair with the minimum distance between points:

dist = lambda s,d: (s[0]-d[0])**2+(s[1]-d[1])**2

I have a dictionary, origin:

{u'toid': u'osgb4000000029928750', u'point': [524511.405, 184846.794]}

I have another list containing pairs of coordinates, d_origins:

[(532163.5648939193, 181848.77608212957),(532449.8292416488, 181847.71793660522), (532200.2156880093, 182053.30247829395), (533794.6284605444, 181119.5631480558)]

I then attempt to find the match value by calling the dist lambda function:

match = min((origin[0]['point']),key=partial(dist,d_origins))
print origins, match

however, the output is:

TypeError: 'float' object has no attribute '__getitem__'

Answer 1

The min function takes a list or iterable. Additionally the ordering can be specified by a function with one argument. That means the function maps an element to a value, which is then compared by the min function to find the minimum element.

match = min(d_origins, key=lambda p: dist(p, origin['point']))

The lambda expression wraps the dist function with two arguments to a function with one argument by providing one of the arguments. The new anonymous function compares a coordinate with the specific origin in the lambda expression. Then, the result of the min function is the closest coordinate to this origin.

Full example:

>>> dist = lambda s,d: (s[0]-d[0])**2+(s[1]-d[1])**2
>>> origin = {'toid': 'osgb4000000029928750', 'point': [524511.405, 184846.794]}
>>> d_origins = [(532163.5648939193, 181848.77608212957),(532449.8292416488, 181847.71793660522), (532200.2156880093, 182053.30247829395), (533794.6284605444, 181119.5631480558)]
>>> 
>>> match = min(d_origins, key=lambda p: dist(p, origin['point']))
>>> print(str(match))
(532200.2156880093, 182053.30247829395)