code: public List<ColumnMetaData> differences(Schema schema) {
          List<ColumnMetaData> ret = new ArrayList<>();
          for (int i = 0; i < schema.numColumns(); i++) {
              if (!columnMetaData.contains(schema.getMetaData(i)))
                  ret.add(schema.getMetaData(i));
          }
  
          return ret;
      }
docs: Compute the difference in {@link ColumnMetaData}
  between this schema and the passed in schema.
  This is useful during the {@link org.datavec.api.transform.TransformProcess}
  to identify what a process will do to a given {@link Schema}.
  
  @param schema the schema to compute the difference for
  @return the metadata that is different (in order)
  between this schema and the other schema