Storing a dynamic array of structures

I'm new to Matlab, and I want to do the following.

I have 2500 data points that can be clustered into 10 groups. My aim is to find the top 5 data points of each cluster that is closest to the centroid. To do that, I did the following.

1) Find the distance between each point to each centroid, and allocate the closest cluster to each data point.

2) Store the data point's index (1,...,2500) and the corresponding distance in a cluster{index} array (not sure what data type this should be), where index = 1,2,...,10.

3) Go through each cluster to find the 5 closest data points.

My problem is I don't know how many data points will be stored in each cluster, so I don't know which data type I should use for my clusters and how to add to them in Step 2. I think a cell array may be what I need, but then I'll need one for the data point index and one for the distance. Or can I create a cell array of structure (consisting of 2 members - index and distance). Again, how could I dynamically add to each cluster then?