scripts/builtin/intersect.dml

#-------------------------------------------------------------
#
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.
#
#-------------------------------------------------------------

# Implements set intersection for numeric data  


# INPUT PARAMETERS:
# ---------------------------------------------------------------------------------------------
# NAME            TYPE    DEFAULT     MEANING
# ---------------------------------------------------------------------------------------------
# X               Double  ---         matrix X, set A
# Y               Double  ---         matrix Y, set B
# ---------------------------------------------------------------------------------------------
 
# Output(s)
# ---------------------------------------------------------------------------------------------
# NAME            TYPE    DEFAULT      MEANING
# ---------------------------------------------------------------------------------------------
# R               Double  ---         intersection matrix, set of intersecting items

m_intersect = function(Matrix[Double] X, Matrix[Double] Y)
  return(Matrix[Double] R)
{
  # compute indicator vector of intersection output
  X = (table(X, 1) != 0) 
  Y = (table(Y, 1) != 0)
  n = min(nrow(X), nrow(Y))
  I = X[1:n,] * Y[1:n,]

  # reconstruct integer values and create output
  R = removeEmpty(target=seq(1,n), margin="rows", select=I)
}