How do I find the last number in a string with excel formulas - excel-formula

Question

I'm parsing strings in excel, and I need to return everything through the last number. For example:
Input: A00XX
Output: A00
In my case, I know the last number will be between index 3 and 5, so I'm brute-forcing it with:
=LEFT([#Point],
IF(SUM((MID([#Point],5,1)={"0","1","2","3","4","5","6","7","8","9"})+0),5,
IF(SUM((MID([#Point],4,1)={"0","1","2","3","4","5","6","7","8","9"})+0),4,
IF(SUM((MID([#Point],3,1)={"0","1","2","3","4","5","6","7","8","9"})+0),3,
))))
Unfortunately, I've run into some edge cases where the numbers extended beyond index 5. Is there a generic way to find the last number in a string using excel formulas?
Note:
I've tried =MAX(SEARCH(... but it returns the index of the first number, not the last.

Answer 1

As a starting point: if we know the position of the last number, we can use LEFT to get the string to that point. Suppose that the position is 5:
=LEFT(A1, 5)
But, we don't know the position of the last number. Now, what if the only valid number was 0, and it only appeared once: then we could use FIND to locate the position of the number:
=LEFT(A1, FIND(0, A1))
But, we have more than one valid number. Suppose that we had all the numbers from 0 through 9, but each number could only appear once — then we could use MAX on a FIND array, to tell us which of the numbers is the last one:
=LEFT(A1, MAX(FIND({0,1,2,3,4,5,6,7,8,9}, A1)))
Unfortunately, FIND will throw a #VALUE! error any number doesn't appear, which will then make MAX return the same error. So, we need to fix that with IFERROR:
=LEFT(A1, MAX(IFERROR(FIND({0,1,2,3,4,5,6,7,8,9}, A1), 0)))
However, numbers can appear more than once. As such, we need a method to find the last occurrence of a value in a string (since FIND and SEARCH will, by default, return the first occurrence).
The SUBSTITUTE function has 3 mandatory arguments — Initial String, Value to be Replaced, Value to Replace with — and one Optional argument — the occurrence to replace. Normally, this is omitted, so that all occurrences are replaced. But, if we know how many times a character appears in a string, then we can replace just the last instance with a special/uncommon sub-string to search for.
To count how many times a character appears in a String, just start with the length of the String, then subtract the length when you SUBSTITUTE all copies of that character for Nothing:
=LEN(A1) - LEN(SUBSTITUTE(A1, 0, ""))
This means we can now replace the last occurrence of the character with, for example, ">¦<", and then FIND that:
=FIND(">¦<", SUBSTITUTE(A1, 0, ">¦<", LEN(A1) - LEN(SUBSTITUTE(A1, 0, ""))))
Of course, we want to do this for all the numbers from 0 to 9, and take the MAX value (remembering our IFERROR), so we need to put the Array of values back in:
=MAX(IFERROR(FIND(">¦<", SUBSTITUTE(A1, {0,1,2,3,4,5,6,7,8,9}, ">¦<", LEN(A1) - LEN(SUBSTITUTE(A1, {0,1,2,3,4,5,6,7,8,9}, "")))), 0))
Then, we plug that all back into our initial LEFT function:
=LEFT(A1, MAX(IFERROR(FIND(">¦<", SUBSTITUTE(A1, {0,1,2,3,4,5,6,7,8,9}, ">¦<", LEN(A1) - LEN(SUBSTITUTE(A1, {0,1,2,3,4,5,6,7,8,9}, "")))), 0)))

Answer 2

An alternative, assuming that the length of the string in question will never be more than 9 characters (which seems a safe assumption based on your description):
=LEFT(A1,MATCH(0,0+ISERR(0+MID(A1,{1;2;3;4;5;6;7;8;9},1))))
This, depending on your version of Excel, may or may not require committing with CTRL+SHIFT+ENTER.
Note also that the separator within the array constant {1;2;3;4;5;6;7;8;9} is the semicolon, which, for English-language versions of Excel, represents the row-separator. This may require amending if you are using a non-English-language version.
Of course, we can replace this static constant with a dynamic construction. However, since we are already making the assumption that 9 is an upper limit on the number of characters for the string in question, this would not seem to be necessary.

Answer 3

If you have the newest version of Excel, you can try something like:
=LEFT(D1,
LET(x, SEQUENCE(LEN(D1)),
MAX(IF(ISNUMBER(NUMBERVALUE(MID(D1, SEQUENCE(LEN(D1)), 1))), x))))
For example: