Problem comparing value of local macro with strings

[Krista Lane]

Hi all,

I'm trying to loop through a lot of files and perform different sets of commands for files of different years. I found a previous post about comparing the value of local macros with strings, which made me think I could use "~=" as a comparison. Here is my code (in case of confusion, the file name format is "gen YYYY"):

tempfile building
save `building', emptyok
local directories: dir . dirs "*"

foreach d of local directories {
    gen temp= "`d'"
    local files: dir "`d'" files "*.xlsx"
    foreach f of local files {
        di "`f'"
        if "`f'" ~="gen 2014" {
            di "`f'/`d'"
        }
    }
}

This returns:

gen 2001.xlsx
gen 2001.xlsx/Data001
gen 2002.xlsx
gen 2002.xlsx/Data001
...

What am I doing wrong? What does ~= do?

Thanks.

[Nick Cox]

What makes you think you are doing anything wrong?

~= is not equals, just like !=

[Krista Lane]

Oh, I though it was similar to = rather than !=.

I realized I should have typed "gen 2014.xlsx". Once I make that change I see that gen 2014.xlsx/Data001 doesn't display, which makes sense. However, when I run the same code using = instead of ~= (which is what I meant to do) I get the error "type mismatch." Why is Stata no longer able to do the comparison?

[Krista Lane]

Ahhhh, I just realized my mistake. I should have typed ==! Oops!!

[Nick Cox]

One equals sign alone = signals an assignment. Stata is confused, no doubt, but using the wrong operator is what causes the confusion.

== is needed to test equality.