Big-Data-HPC-Platform/docs/ECLLanguageReference/ECLR_mods/Expr-RecordSetOps.xml

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<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
<sect1 id="Record_SetRecord_Set_Operators">
  <title>Record Set<indexterm>
      <primary>Record Set</primary>
    </indexterm> Operators<indexterm>
      <primary>Record Set Operators</primary>
    </indexterm></title>

  <para>The following record set operators are supported (all require that the
  files were created using identical RECORD structures<indexterm>
      <primary>RECORD structure</primary>
    </indexterm>):</para>

  <informaltable colsep="1" frame="all" rowsep="1">
    <tgroup align="left" cols="2">
      <colspec colwidth="94.80pt" />

      <colspec />

      <tbody>
        <row>
          <entry>+</entry>

          <entry>Append all records from both files, independent of any
          order</entry>
        </row>

        <row>
          <entry>&amp;</entry>

          <entry>Append all records from both files, maintaining record order
          on each node</entry>
        </row>

        <row>
          <entry>-</entry>

          <entry>Subtract records from a file</entry>
        </row>
      </tbody>
    </tgroup>
  </informaltable>

  <para>Example:</para>

  <programlisting>MyLayout := RECORD
  UNSIGNED Num;
  STRING Number;
END;

FirstRecSet := DATASET([{1, 'ONE'}, {2, 'Two'}, {3, 'Three'}, {4, 'Four'}], MyLayout);
SecondRecSet := DATASET([{5, 'FIVE'}, {6, 'SIX'}, {7, 'SEVEN'}, {8, 'EIGHT'}], MyLayout);

ExcludeThese := SecondRecSet(Num &gt; 6);

WholeRecSet := FirstRecSet + SecondRecSet;
ResultSet   := WholeRecSet-ExcludeThese;

OUTPUT (WholeRecSet);
OUTPUT(ResultSet);
</programlisting>

  <sect2 id="Prefix_Append_Operator">
    <title>Prefix Append Operator</title>

    <para><emphasis role="bold">(+)
    (</emphasis><emphasis>ds_list</emphasis><emphasis role="bold">)
    [</emphasis><emphasis>, options</emphasis><emphasis role="bold">]
    )</emphasis></para>

    <informaltable colsep="1" frame="all" rowsep="1">
      <tgroup cols="2">
        <colspec colwidth="92.05pt" />

        <colspec />

        <tbody>
          <row>
            <entry><emphasis role="bold">(+)</emphasis></entry>

            <entry>The prefix append operator.</entry>
          </row>

          <row>
            <entry><emphasis>ds_list</emphasis></entry>

            <entry>A comma-delimited list of record sets to append (two or
            more). All the record sets must have identical RECORD
            structures.</entry>
          </row>

          <row>
            <entry><emphasis>options</emphasis></entry>

            <entry>Optional. A comma-delimited list of options from the list
            below.</entry>
          </row>
        </tbody>
      </tgroup>
    </informaltable>

    <para>The prefix append operator <emphasis>(+)</emphasis> provides more
    flexibility than the simple infix operators described above. It allows
    hints and other options to be associated with the operator. Similar syntax
    will be added in a future change for other infix operators.</para>

    <para>The following <emphasis>options</emphasis> may be used:</para>

    <para><emphasis role="bold">[, UNORDERED | ORDERED(</emphasis>
    <emphasis>bool </emphasis><emphasis role="bold">) ] [, STABLE | UNSTABLE ]
    [, PARALLEL [ (</emphasis> <emphasis>numthreads </emphasis><emphasis
    role="bold">) ] ] [, ALGORITHM(</emphasis> <emphasis>name
    </emphasis><emphasis role="bold">) ]</emphasis></para>

    <informaltable colsep="1" frame="all" rowsep="1">
      <tgroup cols="2">
        <colspec colwidth="92.05pt" />

        <colspec />

        <tbody>
          <row>
            <entry><emphasis role="bold">UNORDERED</emphasis></entry>

            <entry>Optional. Specifies the output record order is not
            significant.</entry>
          </row>

          <row>
            <entry><emphasis role="bold">ORDERED</emphasis></entry>

            <entry>Specifies the significance of the output record
            order.</entry>
          </row>

          <row>
            <entry><emphasis>bool</emphasis></entry>

            <entry>When False, specifies the output record order is not
            significant. When True, specifies the default output record
            order.</entry>
          </row>

          <row>
            <entry><emphasis role="bold">STABLE</emphasis></entry>

            <entry>Optional. Specifies the input record order is
            significant.</entry>
          </row>

          <row>
            <entry><emphasis role="bold">UNSTABLE</emphasis></entry>

            <entry>Optional. Specifies the input record order is not
            significant.</entry>
          </row>

          <row>
            <entry><emphasis role="bold">PARALLEL</emphasis></entry>

            <entry>Optional. Try to evaluate this activity in
            parallel.</entry>
          </row>

          <row>
            <entry><emphasis>numthreads</emphasis></entry>

            <entry>Optional. Try to evaluate this activity using
            <emphasis>numthreads</emphasis> threads.</entry>
          </row>

          <row>
            <entry><emphasis role="bold">ALGORITHM</emphasis></entry>

            <entry>Optional. Override the algorithm used for this
            activity.</entry>
          </row>

          <row>
            <entry><emphasis>name</emphasis></entry>

            <entry>The algorithm to use for this activity. Must be from the
            list of supported algorithms for the SORT function's STABLE and
            UNSTABLE options.</entry>
          </row>
        </tbody>
      </tgroup>
    </informaltable>

    <para>Example:</para>

    <programlisting>ds_1 := (+)(ds1, ds2, UNORDERED);
  //equivalent to: ds := ds1 + ds2;        
  
ds_2 := (+)(ds1, ds2);
  //equivalent to: ds := ds1 &amp; ds2;                

ds_3 := (+)(ds1, ds2, ds3);
  //multiple file appends are supported</programlisting>
  </sect2>
</sect1>