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How do I accumulate the results of immediate commands?

Question

I am trying to use Stata to calculate confidence intervals quickly for a large amount of data. I have been using the immediate command cii to calculate each confidence interval, but I do not want to have to retype the results to make use of them. How do I accumulate the results of each calculation automatically into a new dataset?

Answer

You are using Stata as a calculator, typing

 cii means 12 56 34
 cii means 21 65 43 

and so on, where the three numbers are the number of observations, the mean, and the standard deviation in each case.

To accumulate the results, we exploit the fact that cii leaves in its wake not just the printed results but also saved results that can be used either interactively or in a program. We can pick those up and put them in variables as part of a dataset that grows as we calculate.

First, set up the scenery. If you have data in memory, clear the data and type

 set obs 1
 gen N = .
 gen mean = .
 gen se = .
 gen lb = .
 gen ub = .

Then set up a do-file, for example, mycii.do:

 -------------- mycii.do
 noi cii means `1' `2' `3'
 qui replace N = r(N) in l
 qui replace mean = r(mean) in l
 qui replace se = r(se) in l
 qui replace lb = r(lb) in l
 qui replace ub = r(ub) in l
 local n = _N + 1
 qui set obs `n'
 -------------------

The l in the code above, in l, is the letter l (standing for last), not the numeral 1 (which would mean first). In this program, the r( ) are the saved results documented in [R] ci. The `1', `2', and `3' refer to the three numbers supplied to cii means, its arguments in programming jargon.

Now type

 run mycii 12 56 34 
 run mycii 21 65 43

Each time you run this do-file, the last observation (initially also the first) will be replaced, and the number of observations in the dataset will be bumped up by 1.

You can promote your do-file to a program:

 -------------- mycii.ado
 program def mycii 
  version 16  
  cii means `1' `2' `3'
  qui replace N = r(N) in l
  qui replace mean = r(mean) in l
  qui replace se = r(se) in l
  qui replace lb = r(lb) in l
  qui replace ub = r(ub) in l
  local n = _N + 1
  qui set obs `n'
 end 
 -------------------

Then type

 mycii 12 56 34

After the last calculation, you have a new dataset. Delete the last observation, which is all missing values.

The same approach will work with any immediate command. Just write your do-file or program to pick up the saved results as documented in the manual entry on the immediate command.