Identify connected points in a grid

Dear all! I have a grid with 0 and 1. My task is to cluster connected points with 1. For example

00001100
01100001
01110101
01000001

Here there are 4 different clusters. I have create a simple code with cycle, that works fine. But it slows dramatically when I began to use it with large arrays (like 1000x1000) May be it is a simple task, but I still can not find optimal solution. Please, give me an advice.

[Purushottama Rao]

what is the ouput expected?

[Arseny Kubryakov]

The expected output is the consistent number of cluster at every grid point, i.e. for given example this will be

00001100
02200003
02220403
02000003

Answer 1

[Walter Roberson]

bwlabel() or regionprops()

[Arseny Kubryakov]

Thank You! It helps.