How to access a Stream<Tuple>?

[Glenda Karen]

I have a Stream<Tuple> that outputs something like:

[{
  A: -3.82,
  B: -9.9371,
  C: 3.551,
  D: 0.1954,
  Index: 24,
  E:  7.99
}]

I'm wondering how I can get the value for Index?

So I could get an integer returned that equals 24.

Thanks so much!

[Campbell Ritchie]

Is that a Stream or a single [Sex]Tuple[t] object? In the case of Streams, let's imagine you have a List<Sextuplet>:-

List<Integer> indices = sextupletList.stream()
                                     .mapToInt(Sextuplet::getIndex)
                                     .boxed()
                                     .collect(Collectors.toList());

Line 1 creates a Stream<Sextuplet>. I haven't filtered the Stream or selected any of its elements or anything. Simply use all elements.
Line 2 uses the method reference to the getIndex() method, which I presume it has, to get it as an int and the Stream creates an IntStream.
Line 3: The IntStream#boxed() method turns the ints to Integers and creates a Stream<Integer>.
Line 4: You can use a Collector as an argument to the collect() method, but it is easier to go to the Collectors class, which has a method supplying just what you want.

[Piet Souris]

Almost. The link to the API is given here: Tuple

So, instead of the method reference: Tuple::getIndex, it should be

mapToInt(tuple -> tuple.getInt(4))

or

mapToInt(tuple -> tuple.getInt("Index"))

[Glenda Karen]

Thanks so much! I combined both solutions and it worked!

List<Double> who = myDataFrame.stream().filter(row -> row.getString("A").equals(-3.82)).mapToDouble(tuple -> tuple.getDouble("Index")).boxed()
                    .collect(Collectors.toList());

and then I get the value:

double max_N_index = who.get(0);

[Paul Clapham]

The Stream class has a findFirst() method which might be useful, rather than making a List and extracting its first entry.

[Campbell Ritchie]

Glenda Karen wrote:Thanks so much!

That's a pleasure: and well done getting it to work.

. . . .getString("A").equals(-3.82)). . . .

That use of equals() looks dubious to me; maybe you have missed out some quote marks.

[Rob Spoor]

Glenda Karen wrote:

.mapToDouble(tuple -> tuple.getDouble("Index")).boxed()

You can make that slightly shorter by moving the boxing into the mapping, where the double is auto-boxed.

.map(tuple -> tuple.getDouble("Index"))

[Rob Spoor]

Campbell Ritchie wrote:

. . . .getString("A").equals(-3.82)). . . .

That use of equals() looks dubious to me; maybe you have missed out some quote marks.

Campbell's right. That expression always returns false, because a String never equals a Double. Your list will be empty.

[Glenda Karen]

Campbell Ritchie wrote:That use of equals() looks dubious to me; maybe you have missed out some quote marks.

Yes sorry, I had to convert to a string and then was able to use it.

[Glenda Karen]

Rob Spoor wrote:

Glenda Karen wrote:

.mapToDouble(tuple -> tuple.getDouble("Index")).boxed()

You can make that slightly shorter by moving the boxing into the mapping, where the double is auto-boxed.

.map(tuple -> tuple.getDouble("Index"))

Thanks so much, that worked as well!

[Rob Spoor]

You're welcome.