reduce vs foldLeft A big big difference, not mentioned in any other stackoverflow answer relating to this topic clearly, is that reduce should be given a commutative monoid, i.e. an operation that is both commutative and associative. This means the operation can be parallelized. This distinction is very important for Big Data / MPP / … Read more
You will want to use the Aggregate extension method: double product = doubles.Aggregate(1.0, (prod, next) => prod * next); See MSDN for more information. It lets you specify a seed and then an expression to calculate successive values.
You don’t have to reduce an array to get it into a set; just create the set with an array: let objectSet = Set(objects.map { $0.URL }).
Yes, and it’s also called fold in many other programming languages and in Mathematics. Ruby aliases a lot in order to be intuitive to programmers with different backgrounds. If you want to use #length on an Array, you can. If you want to use #size, that’s fine too!
Source Both map and reduce have as input the array and a function you define. They are in some way complementary: map cannot return one single element for an array of multiple elements, while reduce will always return the accumulator you eventually changed. map Using map you iterate the elements, and for each element you … Read more
In addition to what Lee said, you can define reduce in terms of fold, but not (easily) the other way round: let reduce f list = match list with | head::tail -> List.fold f head tail | [] -> failwith “The list was empty!” The fact that fold takes an explicit initial value for the … Read more
The problem is that your accumulator values are promises – they’re return values of async functions. To get sequential evaluation (and all but the last iteration to be awaited at all), you need to use const data = await array.reduce(async (accumP, current, index) => { const accum = await accumP; … }, Promise.resolve(…)); That said, … Read more
UPDATE Some of the commentators make a good point that the original array is being mutated in order to break early inside the .reduce() logic. Therefore, I’ve modified the answer slightly by adding a .slice(0) before calling a follow-on .reduce() step, yielding a copy of the original array. NOTE: Similar ops that accomplish the same … Read more
The Pythonic way of summing an array is using sum. For other purposes, you can sometimes use some combination of reduce (from the functools module) and the operator module, e.g.: def product(xs): return reduce(operator.mul, xs, 1) Be aware that reduce is actually a foldl, in Haskell terms. There is no special syntax to perform folds, … Read more
fold takes an initial value, and the first invocation of the lambda you pass to it will receive that initial value and the first element of the collection as parameters. For example, take the following code that calculates the sum of a list of integers: listOf(1, 2, 3).fold(0) { sum, element -> sum + element … Read more