Package io.deephaven.engine.table

Class MultiJoinFactory

java.lang.Object
io.deephaven.engine.table.MultiJoinFactory
public class MultiJoinFactory extends Object

Join unique rows from a set of tables onto a set of common keys.

The multiJoin operation collects the set of distinct keys from the input tables, then joins at most one row per key from each of the input tables onto the result. Input tables need not have a matching row for each key, but they may not have multiple matching rows for a given key.

Input tables with non-matching key column names must use the JoinMatch format to map keys to the common output table key column names (e.g. "OutputKey=SourceKey"). Also, individual columns to include from input tables may be specified and optionally renamed using JoinAddition format (e.g. "NewCol=OldColName"). If no output columns are specified then every non-key column from the input table will be included in the multi-join output table.

The multiJoin operation can be thought of as a merge of the key columns, followed by a selectDistinct and then a series of iterative naturalJoin operations as follows (this example has common key column names and includes all columns from the input tables): 


     private Table doIterativeMultiJoin(String [] keyColumns, List<? extends Table> inputTables) {
         final List<Table> keyTables = inputTables.stream().map(t -> t.view(keyColumns)).collect(Collectors.toList());
         final Table base = TableTools.merge(keyTables).selectDistinct(keyColumns);

         Table result = base;
         for (int ii = 0; ii < inputTables.size(); ++ii) {
             result = result.naturalJoin(inputTables.get(ii), Arrays.asList(keyColumns));
         }

         return result;
     }

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static interface 
    MultiJoinFactory.Creator
    Creator interface for runtime-supplied implementation.
    static interface 
    MultiJoinFactory.CreatorProvider
    Creator provider to supply the implementation at runtime.

  • Constructor Summary

    Constructors
    Constructor
    Description
    MultiJoinFactory()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    static MultiJoinTable
    of(@NotNull MultiJoinInput... multiJoinInputs)
    Perform a multiJoin for one or more tables; allows renaming of key column names and specifying individual input table columns to include in the final output table.
    static MultiJoinTable
    of(@NotNull String[] keys, @NotNull Table... inputTables)
    Join tables that have common key column names; include all columns from the input tables.
    static MultiJoinTable
    of(@NotNull String columnsToMatch, @NotNull Table... inputTables)
    Join tables that have common key column names; include all columns from the input tables.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • MultiJoinFactory

      public MultiJoinFactory()

  • Method Details

    • of

      public static MultiJoinTable of(@NotNull @NotNull String[] keys, @NotNull @NotNull Table... inputTables)
      Join tables that have common key column names; include all columns from the input tables.

      Parameters:
      keys - the key column pairs in the format "Result=Source" or "ColumnInBoth"
      inputTables - the tables to join together
      Returns:
      a MultiJoinTable with one row for each key and the corresponding row in each input table

    • of

      public static MultiJoinTable of(@NotNull @NotNull String columnsToMatch, @NotNull @NotNull Table... inputTables)
      Join tables that have common key column names; include all columns from the input tables.

      Parameters:
      columnsToMatch - A comma separated list of key columns, in string format (e.g. "ResultKey=SourceKey" or "KeyInBoth").
      inputTables - the tables to join together
      Returns:
      a MultiJoinTable with one row for each key and the corresponding row in each input table

    • of

      public static MultiJoinTable of(@NotNull @NotNull MultiJoinInput... multiJoinInputs)
      Perform a multiJoin for one or more tables; allows renaming of key column names and specifying individual input table columns to include in the final output table.
      Parameters:
      multiJoinInputs - the description of each table that contributes to the result
      Returns:
      a MultiJoinTable with one row for each key and the corresponding row in each input table