Weighted interquartile range

How did you compute the weighted median? According to this Wikipedia page (https://en.wikipedia.org/wiki/Weight...centile_method ), the weighted median is just a special case of the more general weighted percentile formula. I expect that you should be able to substitute something other than 50 or 0.5 (depending on the formula you used for weighted median) and get the desired weighted percentile (if I understand correct, the 25th and 75th percentile). Then compute your interquartile range.

Do you understand how gjlindn's code? It looks like, rather than use the formula described by Wikipedia, his/her UDF simply makes a new array of "weight" copies of each "value". Then uses the built in WorksheetFunction.Median() function to derive the median. By simply changing WorksheetFunction.Median to WorksheetFunction.Percentile() or .Quartile(), you could return any quartile or percentile you wanted from the UDF.

I am hesitant to "just do it for you" because this edit should be very simple. What have you tried, and what has happened with each attempt?

Here's a quick edit allowing you to see how to replace the .Median() function with either the .Quartile() function or the .Percentile() function:

unction WTMEDIAN(ValueRange As Range, WeightRange As Range) As Double
    Dim aArray()   As Variant
    Dim rCell       As Range
    Dim lRowCnt     As Long
    Dim lColCnt     As Long
    Dim lCount      As Long
    Dim lAry        As Long
    
    If ValueRange.Cells.Count = WeightRange.Cells.Count And _
    (ValueRange.Rows.Count = WeightRange.Rows.Count Or _
    ValueRange.Columns.Count = WeightRange.Columns.Count) And _
    ValueRange.Rows.Count * ValueRange.Columns.Count = ValueRange.Cells.Count Then
        ReDim aArray(WorksheetFunction.Sum(WeightRange) - 1)
        lRowCnt = 1
        lColCnt = 1

'This block "unwinds" the weighted array into a single array with weight copies of each value
'The outer rcell loop loops through each weight in weight range
        For Each rCell In WeightRange
'The inner lCount loop makes weight (the value in rCell) copies of the corresponding value in ValueRange
            For lCount = 1 To Int(rCell)
                Debug.Print ValueRange.Item(lRowCnt, lColCnt)
                aArray(lAry) = ValueRange.Item(lRowCnt, lColCnt)
                lAry = lAry + 1
            Next
            If ValueRange.Rows.Count = 1 Then lColCnt = lColCnt + 1
            If ValueRange.Columns.Count = 1 Then lRowCnt = lRowCnt + 1
        Next
'stop function pauses execution and enters debug mode, so you can step through subsequent
'statements and see what happens
stop


'With the weighted values unwound into a simple array of values, use the MEDIAN() worksheet function to get the median
        WTMEDIAN = WorksheetFunction.Median(aArray)

'The same value could be obtained from the QUARTILE() function
         WTMEDIAN=WorksheetFunction.Quartile(aArray,2)
'Of course, the QUARTILE() function can return more than just the median/2nd quartile. You can also return the 1st and/or 3rd quartiles s as well

'or from the PERCENTILE() function
          WTMEDIAN=WorksheetFunction.Percentile(aArray,0.5)
'Of course, the PERCENTILE() function is not limited to the median/50th percentile. It can return any percentile including the 25th and 75th percentiles.

    End If
End Function

Does that help you see how to use these functions in the UDF?