Manipulating arrays without loops

Question

Learning VBA for Excel, I am trying to do as much of my coding without the use of loops. As an exercise, multiplying the numbers of two adjacent ranges, I came up with this:

Sub multiply_range()

Dim a, b, c As Range
Set a = Range("a1:a5")
Set b = Range("b1:b5")
Set c = Range("c1:c5")

a.Value = Evaluate("row(" & a.Address & ")")
b.Value = Evaluate("row(" & b.Address & ")")
c.Value = Evaluate(a.Address & "*" & b.Address)

End Sub

Which works quite nicely. Now I want to do something similar but using arrays instead. Starting with this code:

Sub multiply_array()

Dim aArr(), bArr(), cArr()
ReDim aArr(5), bArr(5), cArr(5)

For i = 0 To 4
    aArr(i) = i + 1
    bArr(i) = i + 1
Next

For i = 0 To 4
    cArr(i) = aArr(i) * bArr(i)
Next

For i = 0 To 4
    Range("D" & i + 1).Value = cArr(i)
Next

End Sub

How would you replace any one of these FOR loops with code that doesn't use loops?

Answer 1

Here you go:

Sub Squares()
    Dim n&
    n = 5
    [d1].Resize(n) = Evaluate("row(1:" & n & ")^2")
End Sub

UPDATE

Here is a variant that uses no loops and no ranges:

Sub Squares()
    Dim a, b, n&
    n = 5
    a = Array(1, 2, 3, 4, 5)
    b = Array(1, 2, 3, 4, 5)
    [d1].Resize(n) = Evaluate("{" & Join(a, ";") & "}*{" & Join(b, ";") & "}")
End Sub

Answer 2

For multiplying arbitrary arrays you can try pasting this code in a new module:

Dim X, Y

Sub MultiplyArrays()
Dim Z
X = Array(1, 2, 3, 4, 5)
Y = Array(1, 2, 3, 4, 5)
Z = [GetX()*GetY()]
Range("D1").Resize(UBound(Z)) = Application.Transpose(Z)   
End Sub

Function GetX()
GetX = X
End Function

Function GetY()
GetY = Y
End Function

Another slightly trickier way is to use worksheetfunction methods:

Sub MultiplyArrays2()
Dim X, Y, Z
X = Array(1, 2, 3, 4, 5)
Y = Array(1, 2, 3, 4, 5)
With Application
    Z = .PV(, 1, .PV(, X, Y))
    Range("D1").Resize(UBound(Z)) = .Transpose(Z)
End With
End Sub

Also see: Adding or multiplying variants in VBA

Answer 3

You can create a couple of helper-functions inspired by functional programming. You can store these in a module (together with other functions for manipulating arrays) and import them as needed.

Function Map(f As String, A As Variant) As Variant
    'assumes that A is a 1-dimensional variant array
    'and f is the name of a function that can be applied to it

    Dim i As Long
    Dim M As Variant

    ReDim M(LBound(A) To UBound(A))
    For i = LBound(A) To UBound(A)
        M(i) = Application.Run(f, A(i))
    Next i
    Map = M
End Function

Function ZipWith(f As String, A As Variant, B As Variant)
    'assumes that A,B are 1-dimensional variant arrays with the same bounds
    'and f is the name of a function with two variables
    Dim i As Long
    Dim M As Variant

    ReDim M(LBound(A) To UBound(A))
    For i = LBound(A) To UBound(A)
        Select Case f:
            Case "+":
                M(i) = A(i) + B(i)
            Case "-":
                M(i) = A(i) - B(i)
            Case "*":
                M(i) = A(i) * B(i)
            Case "/":
                M(i) = A(i) / B(i)
            Case "&":
                M(i) = A(i) & B(i)
            Case "^":
                M(i) = A(i) ^ B(i)
            Case Else:
                M(i) = Application.Run(f, A(i), B(i))
        End Select
    Next i
    ZipWith = M
End Function

Tested like thus:

Function square(x As Variant) As Variant
    square = x * x
End Function

Sub test()
    Dim A As Variant, B As Variant, squares As Variant, products As Variant

    A = Array(2, 3, 4)
    B = Array(5, 6, 7)

    squares = Map("square", A)
    products = ZipWith("*", A, B)

    Debug.Print Join(squares, " ")
    Debug.Print Join(products, " ")
End Sub

Note the absence of loops in the test sub. Output is as expected:

4 9 16
10 18 28