Replace multiple words on string using Map of replacements

Question

I have a map of replacements

val replacements = Map( "aaa" -> "d", "bbb" -> "x", "ccc" -> "mx")

I would like to replace all occurrences of each map key in the string with the corresponding value.

val str = "This aaa is very bbb and I would love to cccc"
val result = cleanString(str, replacements)
result = "This d is very x and I would love to mx"

I have done

val sb = new StringBuilder(str)
for(repl <- replacements.keySet) yield {
  sb.replaceAllLiterally(repl, replacement.get(repl))
}

but I would like something more functional like a map or fold where the function I apply to the string returns another string without needing a mutable variable that is modified inside the loop.

Livvi

Answer 1

One option: use foldLeft on the Map with str as the initial parameter:

replacements.foldLeft(str)((a, b) => a.replaceAllLiterally(b._1, b._2))
// res8: String = This d is very x and I would love to mxc

Therein

The issue with this method is that if one of the replacement words is a sub-string of another word, it replaces that. For example if you a word like "aaaple", it will be "dple". Depends on your application, it might or might not become an issue. – Sightly

warning: method replaceAllLiterally in class StringOps is deprecated (since 2.13.2): Use s.replace as an exact replacement – Wells

Answer 2

I don't really like this, but it should work:

str.split(" ").toList.map { s => 
  if(replacements.get(s).isDefined) { 
    replacements(s) 
  } else { 
    s  
  } 
}.mkString(" ")

Wildawildcat

This won't work if I provide a string without spaces. The example I used was for the sole purpose of illustration and easy understanding of the question. – Livvi

I see. Well how would you split words then though? – Wildawildcat

There is not splitting. This is a string replacement problem. If the provided string is a single string, it should replace the whole string if this is in the replacement map. – Livvi

My "not so beautiful" solution would still work in that case though, won't it? – Wildawildcat

My solution works too but that is not the point. Your solution doesn't work if you provide a string without spaces and need to replace substrings. – Livvi

@Wildawildcat you can replace your whole if .. else statement with replacements.getOrElse(s, s) – Pinery

Gosh this is embarrassing! I've used getOrElse trillions of times and forgot about it now. Thanks Cyrille. – Wildawildcat

Answer 3

You can use regex to do that. Be careful about the order.

val str = "aaaaaa"
val relaceMap = Map("aaaaa" -> "C", "a" -> "A", "aaa" -> "B")
val pattern = relaceMap.keys.mkString("|").r
val result = pattern.replaceAllIn(str, m => relaceMap(m.matched)) // CA

Baroness