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Re: Can I put a filter into a lambda?

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On 12/4/2017 8:03 AM, Eric Douglas wrote:
> On Friday, December 1, 2017 at 4:28:26 PM UTC-5, Eric Sosman wrote:
>>       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!
>>
> rowToModelIndex is an ArrayList<Integer>.

     If it *must* be an ArrayList (and not some other kind of List),
you might want to change the last bit to

	.collect(Collectors.toCollection(ArrayList::new));

Although the toList() method appears to use ArrayList anyhow, it
doesn't guarantee to do so -- meaning that it might use some other
List in a future Java, or in circumstances I haven't studies (e.g.,
it might behave differently with a parallel stream).

> Milliseconds do count in a row filtering method which executes thousands of times.

     If performance is important, measure.  Don't guess.

-- 
esosman@comcast-dot-net.invalid
Eleven hundred forty-three 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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