The datastore function does not automatically detect what type of input data it is as state in Getting Started with MapReduce.

Under the Getting Started with MapReduce there is a statement that is not well explained and can cause alot of confusion. Getting Started with MapReduce\Prepare Data -2nd paragraph: "The datastore function automatically determines which type is appropriate for the dataset." When using .mat files as inputs it is only true that it will automatically determine the data type if the .mat file is already structured as key-value pair otherwise datastore will not work and it will give you errors.