ArrayBuffer, Part 2: Updating and Deleting Elements
The Scala ArrayBuffer is mutable, and this video shows a few common ways to update and delete elements in an ArrayBuffer.
How to update ArrayBuffer elements
This section shows examples of how to update ArrayBuffer elements.
Updating existing elements:
val a = (1 to 4).toBuffer // ArrayBuffer(1, 2, 3, 4)
a(2) = 50 // ArrayBuffer(1, 2, 50, 4)
a.update(0, 10) // ArrayBuffer(10, 2, 50, 4)
a.update(3, 40) // ArrayBuffer(10, 2, 50, 40)Appending, prepending, and inserting
Update can also mean append, so here are a few ways to append elements with += and ++=:
val nums = ArrayBuffer(1, 2, 3) # ArrayBuffer(1, 2, 3)
nums += 4 # ArrayBuffer(1, 2, 3, 4)
nums += (5, 6) # ArrayBuffer(1, 2, 3, 4, 5, 6)
nums ++= List(7, 8) # ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8)With appending, inserting, and prepending you can use symbolic method names, or names like these:
append,appendAllinsert,insertAllprepend,prependAll
The symbolic names are typically aliases for named methods like these.
More examples:
val a = ArrayBuffer(1, 2, 3) // ArrayBuffer(1, 2, 3)
a.append(4) // ArrayBuffer(1, 2, 3, 4)
a.appendAll(Seq(5, 6)) // ArrayBuffer(1, 2, 3, 4, 5, 6)
a.clear // ArrayBuffer()
val a = ArrayBuffer(9, 10) // ArrayBuffer(9, 10)
a.insert(0, 8) // ArrayBuffer(8, 9, 10)
a.insertAll(0, Vector(6, 7)) // ArrayBuffer(6, 7, 8, 9, 10)
a.prepend(5) // ArrayBuffer(5, 6, 7, 8, 9, 10)
a.prependAll(Seq(1,2,3,4)) // ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)Updating in place
Because ArrayBuffer is mutable, you can update its elements in place:
// an example ArrayBuffer:
val a = ArrayBuffer.tabulate(10)(i => i + 1) // a: ArrayBuffer(1 .. 10)
a.dropInPlace(1) // ArrayBuffer(2, 3, 4, 5, 6, 7, 8, 9, 10)
a.dropRightInPlace(1) // ArrayBuffer(2, 3, 4, 5, 6, 7, 8, 9)
a.dropWhileInPlace(_ < 4) // ArrayBuffer(4, 5, 6, 7, 8, 9)
a.filterInPlace(_ > 4) // ArrayBuffer(5, 6, 7, 8, 9)
a.mapInPlace(_ * 10) // ArrayBuffer(50, 60, 70, 80, 90)
a.takeInPlace(4) // ArrayBuffer(50, 60, 70, 80)
a.takeRightInPlace(3) // ArrayBuffer(60, 70, 80)
a.takeWhileInPlace(_ < 80) // ArrayBuffer(60, 70)Deleting ArrayBuffer elements
Use methods and approaches like these to delete ArrayBuffer elements:
// -= and --=
val a = ArrayBuffer.range('a', 'h') // ArrayBuffer(a, b, c, d, e, f, g)
a -= 'a' // ArrayBuffer(b, c, d, e, f, g)
a --= Seq('b', 'c') // ArrayBuffer(d, e, f, g)
a --= Set('d') // ArrayBuffer(e, f, g)
// remove
val a = ArrayBuffer.range('a', 'h') // ArrayBuffer(a, b, c, d, e, f, g)
a.remove(0) // ArrayBuffer(b, c, d, e, f, g)
a.remove(2, 3) // ArrayBuffer(b, c, g)
// trimStart and trimEnd
val a = ArrayBuffer.range('a', 'h') // ArrayBuffer(a, b, c, d, e, f, g)
a.trimStart(2) // ArrayBuffer(c, d, e, f, g)
a.trimEnd(2) // ArrayBuffer(c, d, e)
// clear
val a = ArrayBuffer.range('a', 'h') // ArrayBuffer(a, b, c, d, e, f, g)
a.clear // ArrayBuffer[Char] = ArrayBuffer()More details
For MANY more details and examples, see:
