code: private boolean[] computeProjectionMask() {
  		// mask with all fields of the schema
  		boolean[] projectionMask = new boolean[schema.getMaximumId() + 1];
  		// for each selected field
  		for (int inIdx : selectedFields) {
  			// set all nested fields of a selected field to true
  			TypeDescription fieldSchema = schema.getChildren().get(inIdx);
  			for (int i = fieldSchema.getId(); i <= fieldSchema.getMaximumId(); i++) {
  				projectionMask[i] = true;
  			}
  		}
  		return projectionMask;
  	}
docs: Computes the ORC projection mask of the fields to include from the selected fields.rowOrcInputFormat.nextRecord(null).
  
  @return The ORC projection mask.