How do you create a sequence number by unique column variables?

[#1]

How do you create a sequence number by unique column variables?

See attached of example i manually completed but i have lot more to do!

I often get a response written in code or script format which i struggle to understand so appreciate if you could help me understand the solution if one exists.

Thanks in advance!

[#2 · Accepted solution]

 I don't understand your Lot numbers - you appear to treat 2823 different than 2831, but 2831 the same as 2835.  In any case, the attached should be easily modified, depending on how you really want to define unique Lots.  I did it without scripting.  I used a column of 1s which I then use a ColCumulSum function with accepts a By variable (which I use Lot for).

[#3]

Thank you Dale - very effective solution and yes i had made an error in my dataset.