Question

I have this data:

1,           0.,           0.,        1500.
.
.     
21,           0.,        2000.,        1500.
22,           0.,        2100.,        1500.

which I already appended to a list called nodes: nodes[node ID, coord. x, coord. y, coord. z].

Now I want to find the coincident nodes. So I’ve tried:

for data in nodes:
    for data2 in nodes:
        if data2[1]==data[1] and data2[2]==data[2] and data2[3]==data[3] and data[0]<>data2[0]:
            coincident_nodes.append((data[0],data2[0])) 

what happens is that I get for instance: (31, 32) and (32, 31) and I only want (31, 32) or (32, 31), just one combination.

Many thanks.

Answer 1

Something like this will be much faster when there are more than a few nodes

from collections import defaultdict

nd = defaultdict(list)

for item in nodes:
    nd[tuple(item[1:])].append(item[0])

coincident_nodes = [v for k,v in nd.items() if len(v)>1]