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Re: Can I put a filter into a lambda?

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On 12/1/2017 3:52 PM, Eric Douglas wrote:
> I haven't gotten around to mastering the lambda syntax.
> I have a JTable with a custom row sorter building an index of all model rows:
> 
> rowToModelIndex.clear();
> if (modelRowCount > 0) {
>       if (getRowFilter() != null) {
>            for (int r = 0; r < modelRowCount; r++) {
>                 if (include(r)) {
>                      rowToModelIndex.add(r);
>                 }
>            }
>       } else {
>            rowToModelIndex.addAll(Stream.iterate(firstRow, n -> n + 1).limit(modelRowCount).collect(Collectors.toList()));
>       }
> }
> 
> If it's a straight up series it's a lambda.  Can the filter loop be also?  I would guess that would be more efficient.

     It's not clear what your filter loop is actually doing:
the RowFilter seems never to be used, and I can't find any
one-argument include() method in any Java SE (8 or 9) class.
(You also haven't shown what rowToModelIndex is, but I'll
guess it's a Collection<Integer>, possibly List<Integer>).
So I'll restate the problem without the table trappings:

     1) If getRowFilter() returns null, you want a List of
        all the values 0 through modelRowCount-1, in order.

     2) If getRowFilter() returns non-null, you want a List
        of the same values, excluding those for which the
        boolean-valued include(int) method returns false.

     If that's not the goal, read no further.  But if it is
(or is close enough for jazz), both cases can be written
more simply:

	// Case 1:
	rowModelIndex = IntStream.range(0, modelRowCount)
	    .mapToObj(Integer::valueOf)
	    .collect(Collectors.toList());

	// Case 2:
	rowModelIndex = IntStream.range(0, modelRowCount)
	    .filter((value) -> include(value))
	    .mapToObj(Integer::valueOf)
	    .collect(Collectors.toList());

     Final point: If you can't stop worrying about efficiency,
at the very least stop *guessing* about it!

-- 
esosman@comcast-dot-net.invalid
Eleven hundred forty-six days to go.

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Thread

Can I put a filter into a lambda? Eric Douglas <e.d.programmer@gmail.com> - 2017-12-01 12:52 -0800
  Re: Can I put a filter into a lambda? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-01 16:28 -0500
    Re: Can I put a filter into a lambda? Eric Douglas <e.d.programmer@gmail.com> - 2017-12-04 05:03 -0800
      Re: Can I put a filter into a lambda? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-04 08:20 -0500
        Re: Can I put a filter into a lambda? Eric Douglas <e.d.programmer@gmail.com> - 2017-12-04 05:32 -0800
          Re: Can I put a filter into a lambda? Eric Sosman <esosman@comcast-dot-net.invalid> - 2017-12-04 09:29 -0500
            Re: Can I put a filter into a lambda? Eric Douglas <e.d.programmer@gmail.com> - 2017-12-04 07:14 -0800
            Re: Can I put a filter into a lambda? Sebastian <nowhere@nirvana.org> - 2017-12-08 15:00 +0100

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