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Scala: reduceLeft with string

I have a list of integers and I want to create it.

var xs = list(1,2,3,4,5)
(xs foldLeft "") (_+_)               // String = 12345

with foldLeft it works fine, but my question is, does it work with reduceLeft as well? And if so, how?

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2 answers


It cannot work that way with reduceLeft

. Informally, you can view it reduceLeft

as a special case foldLeft

where the accumulated value is of the same type as the elements of the collection. Since in your case the type of the element Int

, and the accumulated value String

, cannot be used reduceLeft

in the way you used foldLeft

.

However, in this particular case, you can simply convert all elements Int

to the String

front and then shrink:



scala> xs.map(_.toString) reduceLeft(_+_)
res5: String = 12345

Note that this will throw an exception if the list is empty. This is another difference from foldLeft

, which handles the empty case just fine (since it has an explicit seed). It's also less efficient because we are creating a whole new collection (of strings) to shrink in place. In general, foldLeft

there is a much better choice here.

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It takes a little work to make sure the types are understood correctly. Expanding them, you could use something like:



(xs reduceLeft ((a: Any, b: Int) => a + b.toString)).toString
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