title: Keras - Callback to calculate variance
body: <p>Is there a possibility to calculate the variance of target values for each batch using keras custom callback?</p>
  
  <p>Maybe in a similar manner to the <a href="https://stackoverflow.com/questions/47079111/create-keras-callback-to-save-model-predictions-and-targets-for-each-batch-durin">Create keras callback to save model predictions and targets for each batch during training</a> ?
  Im using keras from tensorflow backend and python3.</p>
  
  <p>Cheers,</p>
  
  <p>Maks</p>