I was recently asked, “What is a fold in Scala?” I’ve answered this several times at the links below, but the short answer is that if you want to traverse all of the elements in a sequence to return some value, you probably want a fold (or reduce) method. Many times you won’t need to use the fold or reduce methods yourself because they’re implemented in other methods like map, but because folding a list is such a common pattern, it helps to understand Scala’s fold and reduce methods.
I go into great detail about the Scala fold and reduce methods in the following articles:
- Recursion is great, but check out fold and reduce!
- How to walk through a Scala collection with ‘reduce’ and ‘fold’
- A “sum of the squares” algorithm using map/sum and foldLeft
- How to use variable names with the Scala ‘foldLeft’ method
When you’re ready for it, here’s another fold example that’s a little more complicated:
If you want to learn all about fold and reduce in Scala, I hope those examples are helpful.