Re: st: How to make a code faster - alternatives to egen var = concat(vars) ?,

[Antoine Terracol <terracol@univ-paris1.fr>]

Actually it works if the group variables are all positive integers. 
otherwise you would have to deal with the "." for decimal values. 
Doable, but a bit tedious...
Antoine

On 17/06/2010 23:17, Antoine Terracol wrote:
> This might not be the most efficient way, but it works:
>
> capture program drop mymean
> program define mymean, byable(recall)
> syntax varname
> marksample touse
> local groupname ""
> foreach var of local _byvars {
> local a =`var'[_byn1()]
> if "`a'"=="." {
> local a "missing"
> }
> local groupname "`groupname'`a'"
> }
> su `varlist' if `touse'
> scalar mean`groupname'=r(mean)
> end
>
> scalar drop _all
> sysuse auto, clear
> bysort foreign rep78 : mymean price
> scalar dir
>
>
> Antoine
>
>
> On 17/06/2010 16:56, Tiago V. Pereira wrote:
> > Thank you so much again, Antoine!
> >
> > Yes, this is a very efficient way! However, I could not figure out how I
> > can save the combination of the categorical variables that a specific
> > meanX refers to.
> >
> > For example, the commands
> >
> > sysuse auto, clear
> > bysort foreign rep78 : mymean price
> > scalar dir
> >
> > show a list of scalars containing the mean of the ith combination, but I
> > don't know if the mean10 refers to the combination "foreign = Foreign,
> > rep78 =4" or "foreign = Foreign, rep78 = 5"
> >
> >
> > [Actually I do in this specific case if I take a look at each value from
> > the output.]
> >
> > Nevertheless, assuming a very large number of categorical variables
> > (n>10), I cannot write a loop and say that mean2451 refers to the
> > combination x1==0 x2==0 x3==2 x4==0 x5==2 and x6==1. I want to summarize
> > the mean of this combination in group 1 and generate a separate variable
> > for group 2.
> >
> >
> > for example
> >
> > bysort x1 x2 x3 x4 x5 x6 : mymean score if group==1
> >
> > */ yes, -mymean- needs further amendments to have this option
> >
> > replace score = mean2451 if
> > group==2&x1==0&x2==0&x3==2&x4==0&x5==2&and&x6==1
> >
> >
> > So, In this case I know that mean2451 comes from the combination
> > x1==0&x2==0&x3==2&x4==0&x5==2&and&x6==1 from group 1 and I replace its
> > value for all subjects from group 2 having an identical combination.
> >
> >
> > This is getting tough, but you have any additional tips, I will be really
> > very grateful!
> >
> > Thanks again.
> >
> > Tiago
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> >
> > > Tiago,
> > >
> > > You would have to define a -byable- -program-, such as:
> > >
> > > capture program drop mymean
> > > program define mymean, byable(recall)
> > > syntax varname
> > > marksample touse
> > > su `varlist' if `touse'
> > > local a= _byindex()
> > > scalar mean`a'=r(mean)
> > > end
> > >
> > > sysuse auto, clear
> > > bysort foreign rep78 : mymean price
> > > scalar dir
> > >
> > > Antoine
> > >
> > > On 17/06/2010 15:47, Tiago V. Pereira wrote:
> > > > Thanks, Antoine!
> > > >
> > > > But for each combinations, I want to save a local containing the
> > > > r(mean).
> > > > Is it possible to do that using -bysort-?
> > > >
> > > > Tiago
> > > >
> > > >
> > > > ---------------
> > > > Dear statalisters,
> > > >
> > > > I am working on a stata code, and I need some advice.
> > > >
> > > > I have n categorical variables that assumes values equal to 0, 1 or 2.
> > > > My
> > > > objective is to summarize a continuous variable (say, age) by all
> > > > possible
> > > > combinations of these categorical variables.
> > > >
> > > >
> > > > For example, suppose I have 5 categorical variables (x1, x2, x3, x4 and
> > > > x5):
> > > >
> > > >
> > > > sum age if x1==0&x2==0&x3==0&x4==0&x5==0
> > > >
> > > > then
> > > >
> > > > sum age if x1==0&x2==0&x3==0&x4==0&x5==1
> > > >
> > > > then
> > > >
> > > > sum age if x1==0&x2==0&x3==0&x4==0&x5==2
> > > >
> > > > and so forth.
> > > >
> > > >
> > > > What I am doing is the following: (1) I generate a string of the
> > > > categorical variables
> > > >
> > > > egen combination = concat(x1 x2 x3 x4 x5)
> > > >
> > > > (2) convert them to numeric
> > > >
> > > > encode combination, gene (y)
> > > >
> > > > and loop over the values of the new variable y to summarize the
> > > > continuous
> > > > variable
> > > >
> > > > forvalues i = 1/`some_max_value' {
> > > >
> > > > sum age if y=`i'
> > > >
> > > > }
> > > >
> > > > This naïve solution works very well for small samples (_N<1000) and
> > > > small
> > > > number of categorical variables (5 to 7). But when I need
> > > > investigate in
> > > > a
> > > > larger sample with a larger number of categorical variables, this code
> > > > is
> > > > highly inefficient (e.g. slow).
> > > >
> > > > Do you have any suggestions to make this procedure faster in larger
> > > > data
> > > > sets?
> > > >
> > > > Thanks in advance!
> > > >
> > > > Tiago
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > *
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