Unique values from 1D-array, without iteration

Question

At risk of being of topic, I decided to share some code, Q&A-style. If the general opinion is such that this would be off-topic I\'ll be happy to delete if need be.

Answer 1

Approach via FilterXML()

Just to enrich the variety of fine solutions above, I demonstrate an approach via the new worksheet function FilterXML().

Sub testUniqueItems()
'   Purp: list unique items
'   Site: https://stackoverflow.com/questions/59683363/unique-values-from-1d-array-without-iteration
    Dim arr As Variant: arr = Array("A", "A", "C", "D", "A", "E", "G")
'[1]get uniques
    Dim uniques
    uniques = UniqueXML(arr)
'[2]display in Immediate Window: A,A,C,D,A,E,G => A,C,D,E,G
    Debug.Print Join(arr, ",") & " => " & _
                Join(uniques, ",")
End Sub

Function UniqueXML(arr, Optional Delim As String = ",")
  ' Purp: return unique list of array items
  ' Note: optional argument Delim defaulting to colon (",")
  ' Help: https://docs.microsoft.com/de-de/office/vba/api/excel.worksheetfunction.filterxml
  ' [1] get array data to xml node structure (including root element)
    Dim wellformed As String
    wellformed = "" & Join(arr, "") & ""
  ' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ' [2] define XPath string searching unique item values
  ' Note: c.f. udf: https://stackoverflow.com/questions/58677041/vba-excel-how-to-display-non-equal-values-in-an-excel-array/58685756#58685756
  ' ------------------------------------------------
  ' //i                    ... all  node values after the DocumentElement
  ' [not( .=preceding::i)] ... only if not preceded by siblings of the same node value
  ' ------------------------------------------------
    Dim myXPath As String
    myXPath = "//i[not( .=preceding::i)]"
  ' [3a] get (delimiter separated) unique list
    UniqueXML = Evaluate("=TEXTJOIN(""" & Delim & """,,FILTERXML(""" & wellformed & """, """ & myXPath & """))")
  ' [3b] return array
    UniqueXML = Split(UniqueXML, Delim)
End Function

Related links

MS Help

Display non equal values in an Excel array

Caveat

Note that the Worksheet function FilterXML() can be used from vers. 2016+, but TextJoin only in vers. 2019+ (thx @FaneDuru for comments:-)

Furthermore you would have to be aware of the limits of evaluate. 255 chars only (thx @JvDv).

To overcome both obstacles I reworked above function to work in versions 2016+, too.

Modified function /Edit as of 2020-08-20

Function UniqueXML(arr, Optional Delim As String = ",")
  ' Purp: return unique list of array items
  ' Note: optional argument Delim defaulting to colon (",")
  ' Help: https://docs.microsoft.com/de-de/office/vba/api/excel.worksheetfunction.filterxml
  ' [1] get array data to xml node structure (including root element)
    Dim wellformed As String
    wellformed = "" & Join(arr, "") & ""
  ' ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  ' [2] define XPath string searching unique item values
  ' Note: c.f. udf: https://stackoverflow.com/questions/58677041/vba-excel-how-to-display-non-equal-values-in-an-excel-array/58685756#58685756
  ' ------------------------------------------------
  ' //i                    ... all  node values after the DocumentElement
  ' [not( .=preceding::i)] ... only if not preceded by siblings of the same node value
  ' ------------------------------------------------
    Dim myXPath As String
    myXPath = "//i[not( .=preceding::i)]"
   
  ' [3] get "flat" 1-dim array (~> one-based!)
    Dim tmp As Variant
    tmp = Application.Transpose(WorksheetFunction.FilterXML(wellformed, myXPath))
'  ' [3a] optional redim as zero-based array
'    ReDim Preserve tmp(LBound(tmp) - 1 To UBound(tmp) - 1)
        
  ' [4] return function result
    UniqueXML = tmp
End Function