st: Invalid Syntax - Drop

[Socrates Mokkas <socrates.mokkas@economics.oxford.ac.uk>]

Hello All, 

I have a problem with dropping variables. This is my small loop:

foreach var of varlist cross* {
	qui su `var'
	drop `var' if `r(max)'==0
}

Why is the invalid syntax comming up? What I want to do is to drop variables ( included in the varlist cross*) if they have values only of zeros or missing values. Am I missing the obvious here?

Thanks a lot!

Regards, 
Socrates
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