ceph/src/arrow/ruby/red-arrow/lib/arrow/rolling-window.rb

   1 # Licensed to the Apache Software Foundation (ASF) under one
   2 # or more contributor license agreements.  See the NOTICE file
   3 # distributed with this work for additional information
   4 # regarding copyright ownership.  The ASF licenses this file
   5 # to you under the Apache License, Version 2.0 (the
   6 # "License"); you may not use this file except in compliance
   7 # with the License.  You may obtain a copy of the License at
   8 #
   9 #   http://www.apache.org/licenses/LICENSE-2.0
  10 #
  11 # Unless required by applicable law or agreed to in writing,
  12 # software distributed under the License is distributed on an
  13 # "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
  14 # KIND, either express or implied.  See the License for the
  15 # specific language governing permissions and limitations
  16 # under the License.
  17
  18 module Arrow
  19   # Experimental
  20   #
  21   # TODO: Almost codes should be implemented in Apache Arrow C++.
  22   class RollingWindow
  23     def initialize(table, size)
  24       @table = table
  25       @size = size
  26     end
  27
  28     def lag(key, diff: 1)
  29       column = @table[key]
  30       if @size
  31         windows = column.each_slice(@size)
  32       else
  33         windows = column
  34       end
  35       lag_values = [nil] * diff
  36       windows.each_cons(diff + 1) do |values|
  37         target = values[0]
  38         current = values[1]
  39         if target.nil? or current.nil?
  40           lag_values << nil
  41         else
  42           lag_values << current - target
  43         end
  44       end
  45       ArrayBuilder.build(lag_values)
  46     end
  47   end
  48 end