Unknown stata command in rangejoin

[Marc Pelow]

Hi,

I came across the following command:

rangejoin DateStartRole . Deal_Announced using temp_director_histories, by(DirectorID)

Where DateStartRole is the start date of a directors job in a company, Deal_Announced is the announcement date of an M&A transaction and DirectorID is the ID of the specific director.
I was asking myself what the "." is supposed to do in the code? According to the rangejoin syntax, it represents the low boundary, whereas DateStartRole is the key variable and Deal_Announced the upper boundary.
I suppose the "." is a general stata command here, as I couldn't find ich using the help file of rangejoin.
Thanks

[Nick Cox]

The isolated dot or period is not a Stata command.

Its customary meaning is numeric missing, so that . means "missing, and considered larger than any specified numeric value" but in some Stata commands it has a connotation that is more like "unknown" or even "whatever fits here" or even "as small as possible".

A relatively simple example of the latter is in graph axis scale options where say ysc(r(. 100)) means "stretch the y axis so that its maximum is 100, so long as that includes all data, but leave the minimum as you would calculate otherwise".

The example is germane here as rangejoin (from SSC, as you are asked to explain) is using essentially the same idea.

The explanation in the help file is a terser version of this:

Finally, you can specify low or high using a system missing value, in which case the bound for each
observation will be missing.

More at

help missing

[Marc Pelow]

Dear Nick,
thank you very much for the clarification. That helped a lot.