Truncate text to get preview in Scala - string

Question

I need to truncate a text to get a preview. The preview is the text prefix of ~N chars (but not more) and it should not split words in the middle.
preview("aaa", 10) = "aaa"
preview("a b c", 10) = "a b c"
preview("aaa bbb", 5) = "aaa"
preview("a b ccc", 3) = "a b"
I coded a function as follows:
def preview(s:String, n:Int) =
if (s.length <= n) s else s.take(s.lastIndexOf(' ', n))
Would you change or fix it ?
Now I am thinking how to handle the case when the text words are separated by one or more white spaces (including \n,\t, etc.) rather than just a single space. How would you improve the function to handle this case ?

Answer 1

How about the following:
def preview(s: String, n: Int) = if (s.length <= n) {
s
} else {
s.take(s.lastIndexWhere(_.isSpaceChar, n + 1)).trim
}
This function will:
For the strings shorter or equal n return the string (no preview required)
Otherwise find the the last space character in the n + 1 first characters (this will indicate whether the last world is being split, as if it's not than n + 1 will be a space chracter and otherwise a non-space character) and take a string up to this point
Note: The usage of isSpaceChar will not only provide support for space, but also new line or paragraph, which is what I believe you're after (and you can replace it with isWhitespace if you're after even more extended set of word separators).

Answer 2

I propose next one:
-- UPDATED--
def ellipsize(text : String, max : Int): String = {
def ellipsize0(s : String): String =
if(s.length <= max) s
else {
val end = s.lastIndexOf(" ")
if(end == -1) s.take(max)
else ellipsize0(s.take(end))
}
ellipsize0("\\s+".r.replaceAllIn(text, " "))
}
Or your (modified):
def preview(str : String, n : Int) = {
(s : String) => if (s.length <= n) s else s.take(s.lastIndexOf(' ', n))
}.apply( "\\s+".r.replaceAllIn(str, " "))

Answer 3

How about this
def preview(s:String, n:Int) =
if (s.length <= n) s
else s.take(n).takeWhile(_ != ' ')
Try it here: http://scalafiddle.net/console/a05d886123a54de3ca4b0985b718fb9b

Answer 4

This seems to work:
// find the last word that is not split by n, then take to its end
def preview(text: String, n: Int): String =
text take (("""\S+""".r findAllMatchIn text takeWhile (_.end <= n)).toList match {
case Nil => n
case ms => ms.last.end
})
An alternative take (pun intended) but doesn't like input of all whitespace:
text take (("""\S+""".r findAllMatchIn text takeWhile (m => m.start == 0 || m.end <= n)).toList.last.end min n)
Extensionally:
object Previewer {
implicit class `string preview`(val text: String) extends AnyVal {
// find the last word that is not split by n, then take to its end
def preview(n: Int): String =
text take (("""\S+""".r findAllMatchIn text takeWhile (_.end <= n)).toList match {
case Nil => n
case ms => ms.last.end
})
}
}
Looks nice that way:
class PreviewTest {
import Previewer._
#Test def shorter(): Unit = {
assertEquals("aaa", "aaa" preview 10)
}
#Test def spacey(): Unit = {
assertEquals("a b c", "a b c" preview 10)
}
#Test def split(): Unit = {
assertEquals("abc", "abc cba" preview 5)
}
#Test def onspace(): Unit = {
assertEquals("a b", "a b cde" preview 3)
}
#Test def trimming(): Unit = {
assertEquals("a b", "a b cde" preview 5)
}
#Test def none(): Unit = {
assertEquals(" " * 5, " " * 8 preview 5)
}
#Test def prefix(): Unit = {
assertEquals("a" * 5, "a" * 10 preview 5)
}
}