Sequential numbering based on information in another column

Eric.Stewart71

I'm trying to create a formula (preferably one that can be converted into a column formula) that will generate a sequential Change Order Number based on the position and number of times the Contract # is used in my sheet. I'm attaching a screenshot of what I need the finished product to look like. I'm sure I will need an auto number row in here somewhere and probably a helper column but this one's got me scratching my head.

Thanks for any help!

heyjay

="CO-0" + COUNTIF([Contact #]$1:[Contact #]2, [Contact #]@row) + "-" + [Contact #]@row

Some notes:

1. You need to drag the formula from top. Start of range is anchored to Row 1, and End of range is range at row.
2. The serial CO-0 will need a bit of tweaking to count with leading zeroes.

Here's with the flexible leading zeroes up to 999

="CO-" + 
IF(COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) < 10, "00", 
IF(COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) < 99, "0", "")) + 
COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) + 
"-" + [Contact #]@row

heyjay

="CO-0" + COUNTIF([Contact #]$1:[Contact #]2, [Contact #]@row) + "-" + [Contact #]@row

Some notes:

1. You need to drag the formula from top. Start of range is anchored to Row 1, and End of range is range at row.
2. The serial CO-0 will need a bit of tweaking to count with leading zeroes.

Here's with the flexible leading zeroes up to 999

="CO-" + 
IF(COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) < 10, "00", 
IF(COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) < 99, "0", "")) + 
COUNTIF([Contact #]$1:[Contact #]1, [Contact #]@row) + 
"-" + [Contact #]@row