Stata The Stata listserver
[Date Prev][Date Next][Thread Prev][Thread Next][Date index][Thread index]

st: RE: maximum of a list of values


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: maximum of a list of values
Date   Tue, 28 Jun 2005 20:36:10 +0100

Alas, this is just fantasy syntax.

You imply that it is legal, but 
not giving you what you want, whereas
it is illegal.  

When you write something like this 
in mathematics, you rely on a human 
reader being smart enough to work 
out what should replace those dots. 

Stata requires you to be explicit
about what you want in this case. Your example
might indeed tempt people to think that 
there should be a syntax to cover 
it, but suppose that only 

x1 x2 x3 x4 x5 x7 x8 

exist: should Stata interpret 

max(x1[1,1],...,x8[1,1]) 

as the maximum over those 
that exist, or should it squawk 
that x6 doesn't exist? Also, 
how smart should Stata be about

max(x1[1,1],...,x8[7,7])

in such a situation? 

Once a list gets long, it is better 
to think in terms of a loop, as in 

scalar max = x1[1,1] 
forval i = 2/8 { 
	scalar max = max(scalar(max), x`i'[1,1]) 
} 

That is not much shorter than 

scalar max = max(x1[1,1], x2[1,1], x3[1,1], x4[1,1], x5[1,1], x6[1,1], x7[1,1], x8[1,1]) 

but once you have 80 or 800 items, the loop 
really scores. 

Nick 
n.j.cox@durham.ac.uk 

NEYMOTIN, FLORENCE
 
> also, one more question:
> 
> If I want to get the maximum of the first entry of a bunch of 
> entries, then is there a way to do 
> this in shorthand? i.e. suppose I want the maximum of 
> x1[1,1], x2[1,1], x3[1,1], x4[1,1], x5[1,1], 
> x6[1,1], x7[1,1] x8[1,1], then I thought it was possible to 
> write:  max(x1[1,1],...,x8[1,1]) but 
> this isn't giving me all of the values in between.

*
*   For searches and help try:
*   http://www.stata.com/support/faqs/res/findit.html
*   http://www.stata.com/support/statalist/faq
*   http://www.ats.ucla.edu/stat/stata/



© Copyright 1996–2014 StataCorp LP   |   Terms of use   |   Privacy   |   Contact us   |   What's new   |   Site index