st: Superimposed graphs / selected data / if & by

["Allan Reese (Cefas)" <allan.reese@cefas.co.uk>]

Got the solution for this from Tech Support and it's worth reporting to
make it searchable. 

Tried to add bars to a scatterplot and found this effect with the by()
option using || notation:
Each plot separately obeyed the selection and shows only the requested
levels for the by() variable, but when the two plots are superimposed,
it shows all levels for by().  

[G] manual states || and  ( ) notations for superimposed graphs are
equivalent.  Here they are not.

However, solution is to use ( ) notation and put -if- and -by- outside
the ( ).

Nonsense example:

sysuse sp500
recode volume (min/9999=1) (10000/20000=2) (20000/max=3),  gen(size) 
twoway rbar high low  date  if size<3, by(size) barwidth(.6) name(g1)
scatter     high low  date  if size<3, by(size)              name(g2)
scatter  high low date if size<3, by(size) ||  rbar high low date if
size<3, by(size) barwidth(.6) name(g3)
twoway (scatter  high low date  ) ( rbar high low date , barwidth(.6))
if size<3, by(size) name(g4)

Allan


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