After finding a large set of points I'm now trying to sort them such that:

arr = [(1,2)(1,3)(1,4)(2,1)(2,3)]

becomes:

[[(1,2)(1,3)(1,4)],[(2,1)(2,3)]]

In other words I'm trying to group the points by their x coordinate.

I wrote below function to do this:

def sortPoints(points):
    prev = NULL
    sorted = []
    groupe = []
    for p in points:
        if prev == NULL : prev = p[0]
        if p[0] == prev:
            groupe.append(p)
        else :
            sorted.append(groupe[:])
            del groupe[:]
            prev = p[0]
    return sorted

When I run the code I get an array with sorted points as expected, however, a large part of the points also vanish in the process, and I cannot figure out why.

If anyone could help me, that would be great and very appreciated. Thank you in advance.

CodePudding user response：

As mark suggested you should use itertools.groupby for such cases

from itertools import groupby
arr = [(1,2),(1,3),(1,4),(2,1),(2,3)]
arr.sort(key=lambda x: x[0])
[list(v) for _,v in groupby(arr, lambda y: y[0])]
# output
[[(1, 2), (1, 3), (1, 4)], [(2, 1), (2, 3)]]