st: How to normalize variables in stata

[Xixi Lin <winnielxx@gmail.com>]

Hi,

I am trying to normalize variables, and the following is my code:
foreach x in x1 x2 x3{
gen N_`x' = .
gen mean_`x'=.
gen sd_`x'=.
}
forvalues i=2/120{
foreach x in x1 x2 x3{
qui sum `x' if Period==`i', meanonly
replace mean_`x'=r(mean) if Period==`i'
qui sum `x' if Period==`i', meanonly
replace sd_`x'=r(sd) if Period==`i'
}
}


forvalues i=2/120{
foreach x in x1 x2 x3{
replace N_`x'=(`x'-mean_`x')/sd_`x' if Period==`i'
}
}

however, the above code does not working, because it creates all
missing values for standard deviation. Can anyone help me to fix the
code? Thanks.

Best,
Xixi Lin
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