Generate new variable with 2 decimals in the same command line

[Roman Mostazir]

Dear all,

I am looking for a way of generating a new variable, which is a product of two other variables, with two decimal places. Can I do it in one line command? The generation of the new variable is:

gen newvar=old1*old2

Regards,
Roman

[Nick Cox]

"2 decimals" could be a matter of assigning an appropriate display format afterwards; that can't be done in the same command. Alternatively, if you really mean a string variable, then string(old1 * old2, "%3.2f") should work.

[Roman Mostazir]

Thanks for the information Nick. The variables are numeric. I thought it would be a simple thing to do which I wasn't being able to sort out and now I know it was not simple. Thank you again.

[Svend Juul]

It is simple. It would be more complicated to mix two very different processes in one command:
1: Calculating a numeric variable, with the precision possible.
2: Deciding how many decimals you want to look at today.

I can imagine that with, for example, US Dollars, you want a numeric variable with the precision of cents:

gen usd2 = round(usd,0.01)

[Nick Cox]

The round() suggestion won't meet this need, although it may appear to.

The key point remains that Stata necessarily uses binary representations internally and only some integers x, x = 0(1)100, yield decimals x/100 which also have exact binary representations, namely x = 0, 50, 25 and 75. So, Stata has to get as close as it can to approximations of the others.

 
. clear 

. set seed 2803 

. set obs 20
obs was 0, now 20

. gen y = round(runiform(), 0.01) 

. format y %23.18f

. sort y

. l y

     +----------------------+
     |                    y |
     |----------------------|
  1. | 0.119999997317790990 |
  2. | 0.129999995231628420 |
  3. | 0.150000005960464480 |
  4. | 0.209999993443489070 |
  5. | 0.219999998807907100 |
     |----------------------|
  6. | 0.259999990463256840 |
  7. | 0.259999990463256840 |
  8. | 0.300000011920928960 |
  9. | 0.330000013113021850 |
 10. | 0.469999998807907100 |
     |----------------------|
 11. | 0.550000011920928960 |
 12. | 0.639999985694885250 |
 13. | 0.670000016689300540 |
 14. | 0.829999983310699460 |
 15. | 0.889999985694885250 |
     |----------------------|
 16. | 0.939999997615814210 |
 17. | 0.939999997615814210 |
 18. | 0.939999997615814210 |
 19. | 0.990000009536743160 |
 20. | 1.000000000000000000 |
     +----------------------+

Stata just can't hold numbers like 0.12, 0.13, 0.15 exactly to 2 d.p. That's one reason for display formats, naturally.

[Roman Mostazir]

Thanks to both of you for your valuable comments.