shuffle

Shuffle data in minibatchqueue

Since R2020b

Syntax

shuffle(mbq)

Description

shuffle(mbq) resets the data held in mbq and shuffles it into a random order. After shuffling, the next function returns different mini-batches. Use this syntax to reset and shuffle your data after each training epoch in a custom training loop.

Examples

Differences Between shuffle and reset

The shuffle function resets and shuffles the minibatchqueue object so that you can obtain data from it in a random order. By contrast, the reset function resets the minibatchqueue object to the start of the underlying datastore.

Create a minibatchqueue object from a datastore.

ds = digitDatastore;
mbq = minibatchqueue(ds,MiniBatchSize=256)

mbq = 
minibatchqueue with 1 output and properties:

   Mini-batch creation:
               MiniBatchSize: 256
            PartialMiniBatch: 'return'
                MiniBatchFcn: 'collate'
    PreprocessingEnvironment: 'serial'

   Outputs:
                  OutputCast: {'single'}
             OutputAsDlarray: 1
             MiniBatchFormat: {''}
           OutputEnvironment: {'auto'}

Obtain the first mini-batch of data.

X1 = next(mbq);

Iterate over the rest of the data in the minibatchqueue object. Use hasdata to check if data is still available.

while hasdata(mbq)
    next(mbq);
end

Shuffle the minibatchqueue object and obtain the first mini-batch after the queue is shuffled.

shuffle(mbq);
X2 = next(mbq);

Iterate over the remaining data again.

while hasdata(mbq)
    next(mbq);
end

Reset the minibatchqueue object and obtain the first mini-batch after the queue is reset.

reset(mbq);
X3 = next(mbq);

Check whether the mini-batches obtained after resetting or shuffling the minibatchqueue object are the same as the first mini-batch after the minibatchqueue object is created.

isequal(X1,X2)
isequal(X1,X3)

ans = 
   0
ans = 
   1

The reset function returns the minibatchqueue object to the start of the underlying data, so that the next function returns mini-batches in the same order each time. By contrast, the shuffle function shuffles the underlying data and produces randomized mini-batches.

Input Arguments

mbq — Mini-batch queue

minibatchqueue object

Mini-batch queue, specified as a minibatchqueue object.

Version History

Introduced in R2020b