Subtracting Variables Stata

[Jeffrey Riesmeijer]

Dear Stata experts,

I have a question regarding a subtracting. My data looks like this:

A . B . C
x | x
x | x
x | x
x | x
x | x
x | 4
x | x
5 | x
x | x
x | 2
x | x
3 | x
x | 1
x | x
2 | x

I need to get C = A-B but the 'x" are empty cells.
I need: 5-4 = 1, 3-2=1 & 2-1=1 in the C column

Thanks in advance,

Jeff

[Marcos Almeida]

Hello Jeffrey,

Welcome to the Stata Forum.

Please present the data under CODE delimiters or use the SSC - dataex - , as recommended in the FaQ.

That said, I did not get your point in terms of presenting the "rule" so as Stata performs the estimations.

Best,

Marcos

[Nick Cox]

Please do read FAQ Advice #12 on presenting data examples that can be read directly into Stata. This one requires some engineering before it can be handled. Please respect requests made on behalf of those willing to give some time to help you. http://www.statalist.org/forums/help#stata

If a student presented such a dataset I would have to ask how it got this way and what else might be messed up and how you are confident that values are paired like that. Or (more positively) is there some other information that makes this seem natural?

You ask for A - B but all your examples are B - A.

All serious questions, but a literal answer to your example is

clear
input A B
 . .
 . .
 . .
 . .
 . .
 . 4
 . .
5 .
 . .
 . 2
 . .
3 .
 . 1
 . .
2 .
end

gen long obsno = _n
gen OK = (A < .) | (B < .)
bysort OK (obsno) : gen pair = ceil(_n/2)

bysort OK pair (obsno) : gen C = A[2] - B[1]
list, sepby(pair)

     +-------------------------------+
     | A   B   obsno   OK   pair   C |
     |-------------------------------|
  1. | .   .       1    0      1   . |
  2. | .   .       2    0      1   . |
     |-------------------------------|
  3. | .   .       3    0      2   . |
  4. | .   .       4    0      2   . |
     |-------------------------------|
  5. | .   .       5    0      3   . |
  6. | .   .       7    0      3   . |
     |-------------------------------|
  7. | .   .       9    0      4   . |
  8. | .   .      11    0      4   . |
     |-------------------------------|
  9. | .   .      14    0      5   . |
     |-------------------------------|
 10. | .   4       6    1      1   1 |
 11. | 5   .       8    1      1   1 |
     |-------------------------------|
 12. | .   2      10    1      2   1 |
 13. | 3   .      12    1      2   1 |
     |-------------------------------|
 14. | .   1      13    1      3   1 |
 15. | 2   .      15    1      3   1 |
     +-------------------------------+

[Jeffrey Riesmeijer]

Thanks a lot for the help!

[Nick Cox]

Correction to #3:

You ask for A - B but all your examples are B - A.

Quite wrong!