How to compare a string with another where the one

问题:

How do I compare these two string :

val a = "fit bit versa"
val b = "fitbit"

another example

val a = "go pro hero 6"
val b = "gopro"

another example

val a = "hero go pro  6"
val b = "gopro"

another example

val a = "hero 6 go pro"
val b = "gopro"

I want to get "true" for the above comparisons but not here:

val a = "vegan protein powder"
val b = "vega"

This should be false.

Currently I am doing:

def matchPattern(a:String, b: String):String=
{
      val dd = a.split(" ")
      val result = dd.map(_.toLowerCase())
      if(result contains b.toLowerCase) true 
      else false
}

This works for last case but not the rest.

Any suggestion ?

回答1:

Here's one approach using sliding(i), where i ranges from 2 to word-count in a, to assemble a list of all possible concatenated adjacent words. It is then checked to see whether b exactly matches any of the elements in the list, as shown below:

def matchPattern(a: String, b: String): Boolean = {
  val words = a.toLowerCase.split("\\s+")

  val concats = (2 to words.size).foldLeft(words)(
    (acc, i) => acc ++ words.sliding(i).map(_.mkString)
  )

  concats contains b.toLowerCase
}

matchPattern("Hero go Pro 6", "gopro")
// res1: Boolean = true

matchPattern("Hero go Pro 6", "gopro6")
// res2: Boolean = true

matchPattern("Vegan protein powder", "vega")
// res3: Boolean = false

回答2:

Here's an approach using for/yield that turned out similar to @leo-c approach. A for is used to generate a sliding window of length i from words to return the original words and combinations.

def matchPattern(a:String, b: String): Boolean =  {
  val words = a.split(" ")

  val combinations = words ++ (for(
    i <- (2 to words.size);
    acc <- words.sliding(i)
  ) yield acc).map(_.mkString)

  combinations.contains(b)
} 

Test cases:

val a = "fit bit versa"
val b = "fitbit"

val c = "go pro hero 6"
val d = "gopro"

val e = "hero go pro  6"  
val f = "gopro"

//false
val g = "vegan protein powder"
val h = "vega"

val i = "foo gopro bar"
val j = "gopro"

val k = "foo go pro hero bar"
val l = "goprohero"

scala> matchPattern(a,b) && matchPattern(c,d) && matchPattern(e,f) &&  !matchPattern(g,h) && matchPattern(i,j) && matchPattern(k,l) 

res175: Boolean = true

回答3:

I think this is a solution to your problem.

def matchPattern(a: String, b: String): Boolean =
  a
    .split("\\s+")
    .tails
    .flatMap(_.inits)
    .exists(_.mkString("") == b)

This will check for any word or sequence of words in a that exactly matches the word in b. It will reject cases where b is embedded in a longer word or sequence of words.

The split call turns the string into a list of words.

The tails call returns all the possible trailing sub-sequences of a list, and inits returns all the leading sub-sequences. Combining the two generates all possible sub-sequences of the original list.

The exist call joins the words together and compares them with the test word.

---

Note that tails and inits are lazy, so they will generate each solution to be tested in turn, and stop as soon as a solution is found. This is in contrast to the solutions using sliding which create every possible combination before checking any of them.

回答4:

Something like this I guess (your requirements are incomplete, so I interpreted them to "match exactly the beginning portion of the given string, ending with whitespace or end of line, except maybe spaces).

  @tailrec
  def matchWords(input: Seq[Char], words: Seq[Char]): Boolean = (input, words) match {
     case (Seq(), Seq() | Seq(' ', _*)) => true
     case (Seq(), _) => false
     case (Seq(a, tail@_*), Seq(b, rest@_*)) if a == b => matchWords(tail, rest)
     case (_, Seq(' ', rest@_*)) => matchWords(input, rest)
     case _ => false
   }