Difference in same column of numbers with a formula

Question

Hi! I am new to jmp and I have a big data set I am working with, and I need to be able to calcuate the difference to help find rainfall for every 15 minutes during the day, the rainful is given in a column that sums it up daily. I have tried doing an if statement, but it seems to be ignoring the second line of code.

Ex:

Daily rain

12:00 AM .01

12:15 AM .03

12:30 AM .07

1 AM .09

I need my new column to say

Rainfall

.01

.02

.04

.02

It starts with if the time contains 12:00 AM then dailyrain = dailyrain.

What should the next time be?

Mark_Bailey · Answer

The previous solution is correct but subscripting the current row is unnecessary as the formula is evaluated row-wise. Specifically,

If( Row() == 1,
	:Rain,
	:Rain - Lag( :Rain )
)

uday_guntupalli · Answer

@hmarek14 ,
       Try the following column formula:

If( Row() == 1,
	:rain,
	:rain[Row()] - Lag( :rain)
)