Finding the Nth Occurrence of a Character

Barry often finds himself wanting to identify the Nth occurrence of a character within a text string. He knows he can use the SEARCH and FIND worksheet functions for finding an initial occurrence, but is unsure how to find, say, the 3rd occurrence of the letter "B" within a text string.

Actually, the SEARCH function could be used to find the desired occurrence, in the following manner:

=SEARCHB("b",G20,(SEARCHB("b",G20,(SEARCHB("b",G20,1)+1))+1))

Notice how the SEARCHB function is used in a nested manner. The formula specifies what is being searched for (the letter "b") and the number of nesting levels indicates which occurrence within the cell you want to find. The formula returns the position of the desired character within the cell.

The problem with such a formula, of course, is that it is difficult to maintain and can quickly get unusable if you want to find, say, the seventh occurrence.

A more flexible formula would be the following:

=FIND(CHAR(1),SUBSTITUTE(A1,"B",CHAR(1),3))

This formula examines the value in A1. It substitutes the CHAR(1) code for the third occurrence of "B" within the cell. The FIND function then looks within the resulting string for the position where CHAR(1) occurs. If the desired occurrence does not exist, then the formula returns a #VALUE error.

If you prefer, you could create a user-defined function that will look for the Nth position of a character. The following is a very simple macro that takes three arguments: the string to be searched, the text to match, and the position desired.

Function FindN(sFindWhat As String, _
  sInputString As String, N As Integer) As Integer
    Dim J As Integer

    Application.Volatile
    FindN = 0
    For J = 1 To N
        FindN = InStr(FindN + 1, sInputString, sFindWhat)
        If FindN = 0 Then Exit For
    Next
End Function

The function is case sensitive in what it searches for, and it returns the position within the specified string at which the sFindWhat value occurs. If there is no occurrence at the specified instance, then the function returns a 0. The following shows how the function can be used in a worksheet:

=FindN("b",C15,3)