Question

In Mathematica I have a list of point coordinates

size = 50;
points = Table[{RandomInteger[{0, size}], RandomInteger[{0, size}]}, {i, 1, n}];

and a list of cluster indices these points belong to

clusterIndices = {1, 1, 1, 1, 1, 1, 1, 2, 2, 1, 2, 1, 2, 1, 1, 1, 1, 1, 1, 1};

what is the easiest way to split the points into two separate lists based on the clusterIndices values?

EDIT:
The solution I came up with:

pointIndices =
  Map[#[[2]] &,
    GatherBy[MapIndexed[{#1, #2[[1]]} &, clusterIndices], First],
    {2}];
pointsByCluster = Map[Part[points, #] &, pointIndices];

It there a better way to do this?

Answer 1

How about this?

points[[
    Flatten[Position[clusterIndices, #]]
    ]] & /@
 Union[clusterIndices]