Re: st: Use matrix for save results of looping

[Nick Cox <njcoxstata@gmail.com>]

Various fixes to your code are included here.

clear all
set mem 800m
global path "E:/data/ENE"
global pathdo "C:/gonzalo/"
cd "${path}"
local bases ond1996 ond1997
local nbases : word count `bases'
matrix P = J(`nbases',1,.)
matrix rowname P = `bases'
matrix colname P = Junior

local i = 1
foreach base of local bases {
	use `base', clear
	summ p12_2 if p12_2>48
	local hora=r(sum_w)
	summ estado if estado==1
	matrix P[`i',1] = `hora'/r(sum_w)*100
	local ++i
}

matrix list P, format(%2.1f)

Main points:

1. You should set up a matrix of the right size first, then fill in
its results.

2. I guess that you want display to 1 decimal place, but
-round(<whatever>, 0.1)- cannot produce that reliably for reasons
explained in many places under the heading "precision". See e.g. Bill
Gould's blog posts on precision at blog.stata.com

3. For export, see -mat2txt- from SSC.

Secondary points:

4. Forward slashes are safer, even under Windows.

SJ-8-3  pr0042  . . . . . . .  Stata tip 65: Beware the backstabbing backslash
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q3/08   SJ 8(3):446--447                                 (no commands)
        tip to use forward slash instead of backslash for
        directory and file names

5. Don't evaluate macros when you don't need to.

SJ-8-4  pr0045  . . . . . . . . Stata tip 70: Beware the evaluating equal sign
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q4/08   SJ 8(4):586--587                                 (no commands)
        tip explaining the pitfall of losing content in a macro
        because of limits on the length of string expressions

6. Various simplifications included in the code above.

Nick

On Sun, Sep 30, 2012 at 4:15 PM, Gonzalo DURAN SANHUEZA <giduran@puc.cl> wrote:
> by each database, I want save one scalar in a
> unique matrix. I use a foreach command for load each database. The
> problem with my instruction is that only retrieves the scalar for the
> latest database. I need two things: 1) a unique matrix that retrieves
> the scalars defined in all the loop and 2) if exist some instruction
> for   export the matrix into a csv file. Thanks
>
> This is the do
>
> clear all
> set mem 800m
> global path="E:\data\ENE"
> global pathdo="C:\gonzalo\"
> cd "${path}"
> local bases ond1996 ond1997
>
> foreach base of local bases {
>    if "`base'"=="ond1996" {
>       use ond1996, clear
>    }
>    if "`base'"=="ond1997" {
>       use ond1997, clear
>    }
> summ p12_2 if p12_2>48
> local hora=r(sum_w)
> summ estado if estado==1
> scalar k=round(`hora'/r(sum_w)*100, .1)
> matrix define P=(k)
> matrix rowname P=`base'
> matrix colname P=Junior
> matrix list P
> }
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