when you load 'sat.mat' or 'pendigits.mat' into matlab workspace, there are two data matrices and two label vectors,

'train'            
'train_labels'     
'test'             
'test_labels'      

Each row in 'train' or 'test' is a training or testing sample.
'train_labels' and 'test_labels' give corresponding groundtruth labels.
Note There are no examples with class 6 in sat dataset.