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logiccomparison-operatorsstata

Ternary Comparison Operator in Stata?

In my Stata do scripts, I often have to compare dates which may be missing. Unfortunately, the internal representation of . is the largest possible number of the given range, so the following holds:

5 < .

This can become quite annoying e.g. when checking whether a date is within a certain range:

gen between_start_stop     = . if d == .
replace between_start_stop = 1 if ///
    !missing(d) & !missing(start) & !missing(stop) & ///
    start < d & d < stop
replace between_start_stop = 0 if ///
    ((!missing(d) & !missing(start) & !(start < d)) | ///
     (!missing(d) & !missing(stop) & !(d < stop))

instead of the following:

gen between_start_stop = (start < d) & (d < stop)

Is there a way to use comparison operators that work with ternary logic?

I.e., I would like the following statements to be true:

(5 < .) == .
(. < .) == .
(. < 5) == .
(. & 1) == .
(. & 0) == 0
etc...
Solution

  • A couple of suggestions:

    1. use inrange() (also look at inlist) to specify ranges instead of a series of < and > statements;
    2. you can specify multiple items in missing() or !missing() statements like !missing(start, stop, d) and

    3. it really sounds like you want to use cond(), which (using an ex from the help file) can be used to specify multiple conditions in one function:

      g var = 1 if cond(missing(x), ., cond(x>2,50,70))

    returns . if x is missing, returns 50 if x > 2, and returns 70 if x < 2