levelsof returns error "invalid name"

[Ariel Linden]

Hi All,

I am puzzled why levelsof is returning an "invalid name" error for the following:

local trper 1980 1985 1989
levelsof `trper'

or

local trper "1980 1985 1989"
levelsof `trper'

or

local trper "1980 1985 1989"
levelsof  "`trper"'

any help is appreciated!

Thanks,

Ariel

[Nick Cox]

levelsof expects a variable name as the argument following. What you're supplying has unbalanced punctuation, which may be a typo here and not what you're really typing, but Stata is correct that it's not a variable name.

More importantly, what you would expect levelsof to do here? The "levels" of 1980 1985 1989 are just those values.

[Ariel Linden]

Hi Nick!

In this case, the local trper represents an option in a command I am writing (actually modifying a command that you helped me with many moons ago). The user specifies one or more dates (which the option reads as dates).

So in this specific example, local trper has 3 values 1980 1985 and 1989 (whereas in the command the user would set the option to read "trper(1980 1985 1990)".)

My idea here is to first get a count of values in "trper" and then assess whether there are semicolons between them (because the user is required to separate the dates with a semincolon). So ultimately, in this case, the code should first see that there are 3 dates, and then determine if there are 2 semicolons). If not, there is an error...

My block of code looks like this so far:

        levelsof "`trper'"
        local trcnt = r(r)
        if `trcnt' > 1 {
            if `semicnt' != (`trcnt' - 1) {
                di as err "a semicolon ; must separate each date in trperiod()"
                exit 498
            }
        }

I hope my description is clear?

Thanks!

Ariel

[Ariel Linden]

Oops, I forgot to write how I assess `semicnt', which is also a Nick Cox special :-)

/* count of semicolons in trperiod */
local semicnt = length("`trperiod'") - length(subinstr("`trperiod'", ";", "", .))

[Nick Cox]

OK, but as said levelsof can't help you here because it does not extend beyond the levels of a variable.

You need to tokenize using semi-colons.

[Ariel Linden]

Hi Nick,

You're right. I was thinking of using levelsof only as a means of getting to the count of words, but I can get there by:

local trperiod 1980 1985 1989

local trcnt: word count `trperiod'

local semicnt = length("`trperiod'") - length(subinstr("`trperiod'", ";", "", .))

if `trcnt' > 1 {
    if `semicnt' != (`trcnt' - 1) {
       di as err "a semicolon ; must separate each date in trperiod()"
       exit 498
     }
}

Thank you, Nick!

Ariel