st: Stata treatment of sort order

[Andrew Maurer <Andrew.Maurer@qrm.com>]

Hi Statalist,

I'm wondering if anyone can help explain some details about Stata and sorting

First, where does Stata hold information about current sort order? Ie, the extended macro function --`: sortedby'-- returns the current sort order. However, looking at --char dir-- and --macro dir-- I don't see the information there. In particular, I want to overwrite the value, so that --`: sortedby'-- will return the value that I insert. One use might be if I -infile-, and I already know the sort order of the data, but don't want to have to run sort just to populate `: sortedby'. (In --help dta--, I see where it's stored in a physical dta file [<sortlist>sortlist</sortlist>], but it doesn't explain where it is put in memory.

Second, the help file for sort seems somewhat misleading. --help sort-- explains, "Without the stable option, the ordering of observations with equal values of varlist is randomized." What does "randomized" here mean? I interpret it to mean that each residual observation has an equal probability of being in any of the slots specified by the sort list (eg that --sort var1-- is equivalent to --gen rand = runiform()-- --sort var1 rand-- --drop rand-- However, residual sort order doesn't always appear random. For example, if I --sysuse auto--, --sort foreign--, then copy the data to clipboard, --clear--, then use data editor to paste the data back, and finally --sort foreign--, the ordering is always the same as the original ordering (ie: the ordering of observations with equal values of varlist was /not/ randomized.

Is anyone able to explain these observations?

Thank you,

Andrew Maurer 



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