There are Datastores for tabular text files, spreadsheet files, image files, etc. What if my data is a very large binary file, with the format: [size1 X double, size2 X double, ...], while the information of "size1, size2..., offset 1, offset 2..." is stored in a different metafile. I can write my own ReadFcn to load the data into a cell array, each cell is a nX1 double array. but it's way too large to fit the memory. I tried to use filedatastore and define my own Readfcn, but I couldn't use it to access portion of the data like the other datastores. Any suggestions?