Question on reduce function

[Keefetgy]

Hi! Can i check why this code runs into an error?
List.of("abc","def").stream().reduce(0, (x,y) -> x + y.length())

[weiming21]

Hi I believe you would have to add in a combiner for it to work since the x and y in your code are of two different types.
Therefore you could not use the T reduce(T identity, BinaryOperator accumulator) since it works only for the same types and you should use the U reduce(U identity, BiFunction<U, ? super T, U> accumulator, BinaryOperator combiner) method in the java api.

In your case, you can do List.of("abc","def").stream().reduce(0, (x,y) -> x + y.length(), (x,y) -> x + y) as suggested by the lecture slides

[kaitlyngoh]

hi idk if this makes sense but youre taking in and returning 2 different types so you need the accumulator to combine it before you can use the (x, y) -> x + y

[calvinseptyanto]

You need to put the combiner as the third argument, can try "Integer::sum" or (x, y) -> x+y

CMIIW I think it's because the compiler somehow still perceive the output to be "String" per se from ur code, that's why u need to give a combiner to tell the compiler you need to return an integer

[Lu-Yi-Fan]

You are missing a combiner or alternatively you can use the reduce method which only makes use of an identity and an accumulator, i did something like this. I combine the words and then count the length!

int count(List words) {
return words.stream()
.reduce("", (x, y) -> x + y)
.length();
}