Scala: perform multiple maps and flatmaps on a set of strings - scala

Question

I'm pretty new to scala (and programming in general), but have come up with what feels like a less than perfect solution to an issue I have - I was wondering if anyone has a more elegant/efficient one?
I have a (very large) set of strings, a small example of which is below for replication purposes:
val brands = Set("Brand one", "BRAND-two!!!", "brand_Three1, brandThree2", "brand04")
Now what I want to do is clean up this set so that I have a new clean set where:
any strings separated by commas are split into separate strings
leading spaces and non-alphanumeric (and _ -) characters are
removed
any string with a space is replaced by three version of
that string (one with no space, one with "-" instead of a space, and one and one with "_")
The code I have so far does this, but it does it in two steps, thus iterating over the list twice (which is inefficient):
val brands_clean = brands.flatMap(
_.toLowerCase.split(",").map(
_.trim.replaceAll("[^A-Za-z0-9\\-\\_\\s]+", "")
)
)
def spaceVariations(v: String) = if (v.contains(" ")) Set(v.replaceAll(" ", "-"), v.replaceAll(" ", "_"), v.replaceAll(" ", "")) else Set(v)
val brands_final = brands_clean.flatMap(spaceVariations(_))
I have tried incorporating the spaceVariations function directly into the main code by appending to the replaceAll a map or flatMap:
// using the function call
.flatMap(spaceVariations(_))
// or using a function directly within the code
.flatMap {v => if (v.contains(" ")) Set(v.replaceAll(" ", "-"), v.replaceAll(" ", "_"), v.replaceAll(" ", "")) else Set(v) }
but I get the following error:
error: type mismatch;
found : Array[Nothing]
required: scala.collection.GenTraversableOnce[?]
I'm not sure I understand why this doesn't work here, or if there is a better way to achieve what I am trying to achieve?

Answer 1

brands.flatMap(
_.toLowerCase.split(",").map(
_.trim.replaceAll("""[^\w-]""", "")
)
).flatMap(spaceVariations)
Works for me, not sure where (or why) you are getting the error (I cleaned up your regex a little bit to make it more concise, but that shouldn't matter).
Note, that this still traverses the set twice though. Sets are not lazy in scala, so, it will complete the first flatMap with an intermediate set first, and then start with the next one.
If you want to save a scan, you should starts with an Iterator rather than a set, because iterators are lazy, and will send each element through the whole chain before moving on to the next one:
brands
.iterator
.flatMap { _.toLowerCase.split(",") }
.map(_.trim)
.map { _.replaceAll("""[^\w-]""", "") }
.flatMap(spaceVariations)
.toSet

Answer 2

Based on the assumption that your Set will always look like this:
def spaceVariations(v: String) = if (v.contains(" ")) Set(v.replaceAll(" ", "-"), v.replaceAll(" ", "_"), v.replaceAll(" ", "")) else Set(v)
val brands = Set("Brand one", "BRAND-two!!!", "brand_Three1, brandThree2", "brand04")
brands.map( x => if (x.contains(",") ) x.split(",") else x ).flatMap {
case str: String => Array(str)
case a : Array[String] => a
}.map(_.trim.toLowerCase.replaceAll("[^A-Za-z0-9\\-\\_\\s]+", "")).map(spaceVariations(_))
Gives the output :
Set(Set(brand-one, brand_one, brandone), Set(brandthree2), Set(brand04), Set(brand-two), Set(brand_three1))