3 ms·

In his example Array.prototype.reduce, isn't this almost the same as just doing a foreach loop? I don't understand why doing this, it's pretty much the same num

In his example Array.prototype.reduce, isn't this almost the same as just doing a foreach loop? I don't understand why doing this, it's pretty much the same number of lines.

ablomen 9y ago
In this example it is, but a nice thing about using map, reduce etc is that you can chain them together, ex: let out = ["a", "b", "c", 1, 2, 3] // Turn letters to upper case .map(i => { return typeof i === "string" ? i.toUpperCase() : i; }) // Add one to numbers .map(i => { return typeof i === "number" ? i + 1 : i; }) // split letters and numbers up .reduce((all, i) => { typeof i === "string" ? all.letters.push(i) : all.numbers.push(i); return all; }, { "letters": [], "numbers": [] }); // => { letters: ["A", "B", "C"], numbers: [2, 3, 4] }
- Veedrac 9y ago
  Or... you can do all of that in a 4-line loop, without any of the harm to readability or additional code-bloat that's especially important for websites.
- moosingin3space 9y ago
  The problem with this is that it generates two intermediate arrays in the maps, then effectively drops them in the reduce. This may be inefficient. I wish that JavaScript's map/filter/reduce functions returned lazy iterators, like in Rust, so that code like this doesn't produce intermediate arrays. Does anyone know of a library that provides this?
  - marmart 9y ago
    Those intermediate iterations could be dropped by composing the map functions together (same with the reduce), if that really was a performance bottleneck.
    - moosingin3space 9y ago
      With lazy iterators, there is the possibility of better composition of maps/filters/reduces. That's why I'm a fan of the lazy iterators approach -- otherwise the abstraction breaks too easily and it ends up looking like a for-loop anyway.
bestest 9y ago
That's the thing about functional programming. I personally don't remember the last time I had the need to write a foreach loop. Foreach loops even kind of feel _dirty_ to me. All I really need now is Array.map, Array.reduce, Array.filter, Array.sort, Object.keys, Object.values. Reduce is very powerful, you just have to get to know it. Edit: this is how I'd use reduce in this case — https://news.ycombinator.com/item?id=14919636 https://news.ycombinator.com/item?id=14919636 — talk about line numbers
delta1 9y ago
> isn't this almost the same as just doing a foreach loop yes they are both ways of iterating over the array > I don't understand why doing this there's more than one way to skin a cat
keymone 9y ago
foreach implies mutation. reduce is a way to aggregate a collection into single result in an immutable way.

In his example Array.prototype.reduce, isn't this almost the same as just doing a foreach loop? I don't understand why doing this, it's pretty much the same number of lines.

ablomen 9y ago

In this example it is, but a nice thing about using map, reduce etc is that you can chain them together, ex: let out = ["a", "b", "c", 1, 2, 3] // Turn letters to upper case .map(i => { return typeof i === "string" ? i.toUpperCase() : i; }) // Add one to numbers .map(i => { return typeof i === "number" ? i + 1 : i; }) // split letters and numbers up .reduce((all, i) => { typeof i === "string" ? all.letters.push(i) : all.numbers.push(i); return all; }, { "letters": [], "numbers": [] }); // => { letters: ["A", "B", "C"], numbers: [2, 3, 4] }

Veedrac 9y ago
Or... you can do all of that in a 4-line loop, without any of the harm to readability or additional code-bloat that's especially important for websites.
moosingin3space 9y ago
The problem with this is that it generates two intermediate arrays in the maps, then effectively drops them in the reduce. This may be inefficient. I wish that JavaScript's map/filter/reduce functions returned lazy iterators, like in Rust, so that code like this doesn't produce intermediate arrays. Does anyone know of a library that provides this?
- marmart 9y ago
  Those intermediate iterations could be dropped by composing the map functions together (same with the reduce), if that really was a performance bottleneck.
  - moosingin3space 9y ago
    With lazy iterators, there is the possibility of better composition of maps/filters/reduces. That's why I'm a fan of the lazy iterators approach -- otherwise the abstraction breaks too easily and it ends up looking like a for-loop anyway.

bestest 9y ago

That's the thing about functional programming. I personally don't remember the last time I had the need to write a foreach loop. Foreach loops even kind of feel _dirty_ to me. All I really need now is Array.map, Array.reduce, Array.filter, Array.sort, Object.keys, Object.values. Reduce is very powerful, you just have to get to know it. Edit: this is how I'd use reduce in this case — https://news.ycombinator.com/item?id=14919636 https://news.ycombinator.com/item?id=14919636 — talk about line numbers

delta1 9y ago

> isn't this almost the same as just doing a foreach loop yes they are both ways of iterating over the array > I don't understand why doing this there's more than one way to skin a cat

keymone 9y ago

foreach implies mutation. reduce is a way to aggregate a collection into single result in an immutable way.