Slice, substring. A slice is part of a list. It may only contain the elements at positions 4 through 8. A substring is a string slice. It might only contain some characters.
StringOps info. With StringOps in Scala, we apply slice to strings. We take substrings with a start index, and a last index (not a length). List uses the same syntax.
Substring example. In Scala we can call the Substring method as in Java. But a string can also be sliced with the slice function. Some implicit conversions make this possible.
Argument 1 The first character index where we want to start a substring. To get the first character, we use 0.
Argument 2 The last index of our substring. This is not a character count or length—it should be larger than the first argument.
val phrase = "a soft orange cat"// Use slice on a string from scala.collection.immutable.StringOps.// ... Use first index, second index.
val result = phrase.slice(2, 2 + 4)
println("[" + result + "]")[soft]
List example. A list is like a string, but has other types of elements like Ints or Doubles. We can use slice on a list. We use a first and a last index.
Here We begin a slice at the second element (index 1, value 3.5) and continue until the third index.
Next We begin at element 3 (index 2, value 10.3) and continue until the end of the list (with the list's length).
val points = List(1.5, 3.5, 10.3, 11.3)
println(points)
// Get slice of list.
val slice1 = points.slice(1, 3)
println(slice1)
// Get slice until end of list.
val slice2 = points.slice(2, points.length)
println(slice2)List(1.5, 3.5, 10.3, 11.3)
List(3.5, 10.3)
List(10.3, 11.3)
String slice, char. We can access single chars from a string with an index. But with slice, we can get one-char strings (strings of length 1). Strings are sometimes more useful than chars.
Tip The Scala compiler helpfully warns us when we compare a string slice (a substring) to a char.
val letters = "scala"// This is a char.
val result1 = letters(0)
// This is a string.
val result2 = letters.slice(0, 1)
println(result1)
println(result2)
// Cannot compare a char and a string.// ... This always returns false.
println(result1 == result2)C:\programs\program.scala:13: warning:
comparing values of types Char and String using '==' will always yield false
println(result1 == result2)
^
one warning found
s
s
false
Slice versus substring. The slice() and substring methods receive the same arguments. And they return the same results. The returned string parts are equal in this program.
val example = "California"// Slice and substring have the same results on a string.
val firstPart = example.slice(1, 4)
val firstPart2 = example.substring(1, 4)
// Print results.
println(firstPart, firstPart2)
if (firstPart == firstPart2) {
println(true)
}(ali,ali)
true
Performance. I tested the slice method and the substring method on a string. I found the performance was about the same. So we can use either one for top performance.
Version 1 This version of the code uses the slice() method on a string and tests its result.
Version 2 Here we use the substring() method on a string. This code does the same thing as version 1.
Detail The word "substring" makes it clearer what we are trying to do. For this reason is might be a better choice.
val data = "abcdef"// Warm up the JIT.
val test = data.slice(3, 5)
val test2 = data.substring(3, 5)
val t1 = System.currentTimeMillis()
// Version 1: use slice.for (i <- 0 to 100000000) {
val part = data.slice(3, 5)
if (part != "de")
println(false)
}
val t2 = System.currentTimeMillis()
// Version 2: use substring.for (i <- 0 to 100000000) {
val part = data.substring(3, 5)
if (part != "de")
println(false)
}
val t3 = System.currentTimeMillis()
// Print times.
println(t2 - t1)
println(t3 - t2)969 ms, slice
967 ms, substring
A summary. With slice we remove elements from a collection. We specify the elements we want to keep—the rest vanish. An immutable, new collection is returned.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
