mata with if and forevalue

[Clara Etcheverry]

HI!
I have a problem. This is my code :
forvalues p=1/$nb_p {
forvalues i=1/$nb_p {
if pair[`p',1]=pair[`i',1] {
mata somme2`i'=somme-totob`p'
}
}
}

The error is "=exp not allowed
r(101);"

When I write if `p'=`i' or if pair[`p',1]=pair[`i',1] it fails.. but when I write if `p'!=`i' or if pair[`p',1]!=pair[`i',1] there is no error;..
I don't understand why, I am lost...

Thanks!
Clara

[Joseph Coveney]

In Stata, a single equals sign is assignment. To test for equality, you need a double equals sign. Try

if pair[`p',1] == pair[`i',1] {

and see whether that helps.

[Clara Etcheverry]

Oh I was sooo stupid!! Thank you very very much joseph!!

[Joseph Coveney]

No, not stupid.

It's one of the more common errors that I still make when coding hastily, especially when working at the same time in other languages that use the single symbol for both assignment and comparison.

It'd be nicer if Stata's error message added "did you intend '==' ?"

[Clara Etcheverry]

Yes it would be good...