code: public Transform bucket(int numBuckets, String... columns) {
      return LogicalExpressions.bucket(numBuckets,
          JavaConverters.asScalaBuffer(Arrays.asList(columns)).toSeq());
    }
docs: Create a bucket transform for one or more columns.
  <p>
  This transform represents a logical mapping from a value to a bucket id in [0, numBuckets)
  based on a hash of the value.
  <p>
  The name reported by transforms created with this method is "bucket".
  
  @param numBuckets the number of output buckets
  @param columns input columns for the bucket transform
  @return a logical bucket transform with name "bucket"