The LiveCode DataGrid is at once powerful and confounding. Everything is stored in arrays which is fine, but it is fundamentally different than the LiveCode way of doing things in every other way. Make sure you read the documentation for the DataGrid API ...WAY... before you start writing code. Everything your want stored in a DataGrid must be "put" there using DataGrid methods (such as set the dgData of...), otherwise you'll never get it out.
DataGrids = powerful...if you play by the rules.
Read the rules before you start.