ramda transducers with final R.sum

I’m trying to understand Ramda’s transducers. Here’s a slightly modified example from the docs:

const numbers = [1, 2, 3, 4];
const isOdd = (x) => x % 2 === 1;
const firstFiveOddTransducer = R.compose(R.filter(isOdd), R.take(5));
R.transduce(firstFiveOddTransducer, R.flip(R.append), [], R.range(0, 100)); //=> [ 1, 3, 5, 7, 9 ]

But what if I want to sum the elements of the resulting array? The following (just adding R.sum into R.compose) doesn’t work:

const firstFiveOddTransducer = R.compose(R.filter(isOdd), R.take(5), R.sum);

Answer

I’d do something like this, just accumulate on top of an initial 0 value

const list = [1, 2, 3, 4, 5];
const isOdd = R.filter(n => n % 2);

const transducer = R.compose(isOdd);

const result = R.transduce(transducer, R.add, 0, list);

console.log(
  'result',
  result,
);

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Answer