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

RE: st: matrix question


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: matrix question
Date   Fri, 25 Mar 2005 15:38:25 -0000

This is a bit easier in some other software 
than it is in Stata. But is also a bit 
easier than this. I agree with the main 
idea, of looping over rows to select those 
you want, but Paul's example can be condensed 
and then extended a bit roughly along these
lines: 

forval i=1/`=rowsof(mat1)' {
	if mat1[`i',1]==999999 {
		mat mat2 = nullmat(mat2) \ mat1[`i',2]
		local rownames "`rownames' `i'" 
     }
} 
matrix rownames mat2 = `rownames' 

The key details are 

1. use -rowsof()- to work out the number of rows
on the fly. 

2. use -nullmat()- either to initialise or to 
enlarge a matrix 

3. use the loop to select the rownames as well, 
if of interest. 

That said, some canned routines in -matvsort- 
on SSC are other possibilities in nearby terrain. 

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

Paul Millar
 
> As far as I know, there is no easy way to do this in Stata.  
> You will probably need at least 1 loop to do this:
> 
> mat mat2=J(260,1,0)
> local rows=0
> forvalues i=1/260 {
>   if mat1[`i',1]==999999 {
>     local nrows=`nrows'+1
>     mat mat2[`nrows',1]=mat1[`i',2]
>     }
>   }
> di "`nrows' rows updated in mat2"
 
Indranil Majumdar 
 
> > I have a matrix (mat1) with the following data (extract).
> > 
> > . matrix list mat1
> > 
> > mat1[260,2]
> >        ratsect     cutoff
> >  r1     999999  3.435e-06
> >  r2     999999  4.572e-06
> >  r3     999999  6.596e-06
> >  r4     999999  9.606e-06
> >  r5     999999  .00001548
> > r22     999998  5.470e-06
> > r23     999998   .0000119
> > r24     999998   .0000177
> > r25     999998   .0000295
> > r26     999998   .0000439
> > 
> > I want to create another matrix (say mat2) with only those rows 
> > that have a
> > particular 'ratsect' e.g. 999999
> > 
> > I guess the command will look something like the following.
> > matrix mat2 = mat1["some expression ???",2]
> > I am not sure how to filter rows based on a criterion.
> > Any help will be appreciated.

*
*   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