st: Re: efficiency of coding

["Michael Blasnik" <michael.blasnik@verizon.net>]

> I have two questions for you:
<snip>
> ----------------------------------------------------------------
> forvalues i=0(1)2 {
> tempvar temp`i'
> egen `temp`i''=median(`w') if `I`i''
> gsort -`I`i''
> local tempweird=`temp`i''
> scalar lw`i'=log(`tempweird')
<snip>
}

Why not avoid creating the variables?
sum `w' if  `I`i'',detail
scalar lw`i'=r(p50)

> (2)  If I have two matrices A and B, where A is 15x3, and B is 15x1, and I 
> want to make the third column of A EQUAL to the B matrix, is there a quick 
> way to do this?  Right now, I have it replacing value by value in the 
> matrix but I think this is probably slower than it could be.
> The code now looks like:
>
> forvalues i=1(1)15{
> matrix A[`i' , 3]= B[`i',1]
> }
> ----------------------------------------------------------------
> Thanks for your help!
> Florence

It depends on whether A already has a thrid column, sort of.  If there is no 
third column, then you can :

mat A=A,B

otherwise

mat A=A[1...,1..2] , B

You really should just read the on-line help.  whelp matrix would be a good 
start

Michael Blasnik
michael.blasnik@verizon.net

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