Trying to export p values - stata

Question

I'm trying to write a loop to conduct individual t-tests for a list of variables (tab1) and export the means and p-values to Excel using the putexcel command. Right now my code looks like this:
putexcel set "Ttests.xlsx", sheet("t_test") replace
local n_models: word count `tab1'
forval i=1/`n_models' {
mat T=J(`n_models',4,.)
foreach x of tab1 {
ttest `x', by(var)
mat T[`i',1] = r(mu_1)
mat T[`i',2] = r(mu_2)
mat T[`'i,3] = r(mu_1) - r(mu_2)
mat T[`i',4] = r(p)
}
}
putexcel A1= matrix(T)
Unfortunately right now I'm only getting the means/p-values for the first variable of tab1. What am I doing wrong?

Answer 1

This isn't a minimal, complete or verifiable example. See https://stackoverflow.com/help/mcve for the standard here.
There is no data example.
The local macro tab1 isn't defined.
Even with fixes to those, the code is illegal as of tab1 is illegal in the foreach loop and the instruction to put stuff in the third column of the matrix is mangled as the punctuation is wrong. That comes from paraphrasing code, not showing us a version that does what you say.
So, what's key is to show us code that does what you say.
All that said, your problems are conceptual:
Bigger deal 1 You have two nested loops, over a counter and over the variables you want as response. But you need just one loop. You want to loop over the variables and at the same time bump up a counter. Or, you want to loop over a counter and at the same time pick another variable. It doesn't matter which way you do it, at least to Stata.
Bigger deal 2 What happens with (what I guess is) your code? Trace it through. Suppose your number of variables is 4. So, last time around the outer loop, you reset the entire matrix to missings, and then in the inner loop cycle around your variables and each time try to put results for each variable in the 4th row of your matrix (i.e. the same row!). Contrary to your report, I guess that what you see in the spreadsheet is results for the last variable named, not the first.
I think you want code more like this:
sysuse auto, clear
local tab1 mpg price
local var foreign
putexcel set "Ttests.xlsx", sheet("t_test") replace
local n_models: word count `tab1'
mat T = J(`n_models', 4, .)
tokenize `tab1'
forval i=1/`n_models' {
ttest ``i'', by(`var')
mat T[`i',1] = r(mu_1)
mat T[`i',2] = r(mu_2)
mat T[`i',3] = r(mu_1) - r(mu_2)
mat T[`i',4] = r(p)
}
putexcel A1 = matrix(T)