Connecting matrix values with fields in a structure

Hi, I am trying to write a code that matches certain values in a matrix with their corresponding fields when I load in the data.I have an nx3 matrix where the first column is a number grouping the objects in the second and third columns, and the second and third columns are IDs of objects that I want to match to the fields. So my matrix right now is something like

     1   100   100
     1   100   101
     1   100   102
     2   100   100
     2   100   101
     3   101   100
     3   101   101
     3   101   102
     3   101   103
     4   101   100

I am trying to match the IDs in columns 2 and 3 with their corresponding structures S and T respectively, while still keeping the objects together within their group. The objects in the structures S and T are the fields and can be accessed by S.(nms{i}) and T.(names{ii}) where i and ii are the indices of the fields and the names of the fields are nms and names respectively. I want the IDs to correspond to the fields in that 100 = S.(nms{1}) for group 1 (so column 2 rows 1:3) and then 100 = S.(nms{2}) for group 2 (column 2 rows 4 and 5). Then for column 3, 100 = T.(names{1}) for group 1, 101 = T.(names{2}) for group 1 and then 100 = T.(names{4}) for group 2 and so on.

My intention is so that I can run some other code on the objects in the structures for each group. Right now, I have to run my code separately for each group, but I would like to be able to run the code once and have it iterate the code for each group for me. Any help would be appreciated!