Calculating change scores in long format

[Jake Magel]

Hello, I am trying to calculate the change between 2 timepoints for an outcome variable in a long format data file.

I have used the following code to calculate the change between consecutive time points.

xtset record_id time_rc
capt drop ddppq_tot_dlt
gen ddppq_tot_dlt = D.ddppq_tot
replace ddppq_tot_dlt = ddppq_tot_dlt[_n+1] if missing(ddppq_tot_dlt) & record_id == record_id
order ddppq_tot_dlt, after (ddppq_tot)

HOWEVER, I want to now calculate the ddppq_tot change (time_rc == 1 - time_rc == 0 AND time_rc == 2 - time_rc == 0)

I can get the following code to run but, of course, the new variable is deleted from the dataset after running.

preserve
Keep record_id time_rc ddppq_tot
sort record_id time_rc
reshape wide ddppq_tot, i(record_id) j(time_rc)
gen ddppq_tot_d1=ddppq_tot1 - ddppq_tot0
restore

When I run (I have many variables in the dataset):

sort record_id time_rc
reshape wide ddppq_tot, i(record_id) j(time_rc)
gen ddppq_tot_d1=ddppq_tot1 - ddppq_tot0

I get the error: There are variables other than a, b, record_id, time_rc in your data. They must be constant within record_id because that is
the only way they can fit into wide data without loss of information.

The variable or variables listed above are not constant within record_id. Perhaps the values are in error. Type reshape error
for a list of the problem observations.

Either that, or the values vary because they should vary, in which case you must either add the variables to the list of xij
variables to be reshaped, or drop them.

I appreciate any advice.

* Example generated by -dataex-. For more info, type help dataex
clear
input byte record_id float(time_rc freq1_ask_add1)
 1 0 2
 1 1 4
 1 2 5
 2 0 1
 2 1 2
 2 2 2
 3 0 1
 3 1 2
 3 2 2
 4 0 1
 4 1 3
 4 2 3
 5 0 2
 5 1 4
 5 2 4
 6 0 2
 6 1 4
 6 2 6
 7 0 2
 7 1 3
 7 2 3
 8 0 2
 8 1 3
 8 2 3
 9 0 2
 9 1 3
 9 2 4
10 0 1
10 1 2
10 2 2
11 0 2
11 1 5
11 2 4
12 0 2
12 1 5
12 2 6
13 0 3
13 1 4
13 2 4
end