Column counter

[David L]

I am trying to set up a column counter which runs an if
statement depending on how another column data changes.
Data and counter result required is as follows:
counter data
1_1 1
1_2 1
1_3 1
1_4 1
2_1 2
2_2 2
3_1 3
3_2 3
3_3 3

 

[Max]

Assuming the data starts in row2 downwards,

Put in A2: =B2&"_"&COUNTIF($B$2:B2,B2)

Copy A2 down as many rows as there is data in col B

 

[JE McGimpsey]

One way:

A2: =$B2 & "_" & COUNTIF($B$2:$B2,$B2)

copy down as far as necessary.