st: efficiency of coding

["NEYMOTIN, FLORENCE" <neymotin@calmail.berkeley.edu>]

I have two questions for you:

(1) I have a piece of code which I think is probably pretty inefficient and I was wondering 
whether there is a more efficient alternative. I want to have the log of the median of w 
conditional on an indicator being set on (denoted as I0, I1, or I2) saved in a scalar variable.  I 
did this by creating a variable denoting the median and then just setting using the first entry of 
this temporary variable as  the scalar and then using that next value to get the log.  I think 
this is probably really roundabout and not taking advantage of stata's capabilities. thanks! 
Right now, the code looks like:

----------------------------------------------------------------
forvalues i=0(1)2 {

tempvar temp`i'
egen `temp`i''=median(`w') if `I`i''
gsort -`I`i''

*note, the reason this works is because this will always be the first observation after doing the 
sort, and locals get the first value of variable..TRICKY..

local tempweird=`temp`i''

*THIS IS THE MAIN DEFINITION LINE RIGHT HERE
scalar lw`i'=log(`tempweird')


drop `temp`i''
local drop tempweird
}

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(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
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