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

 From "Nick Cox" To Subject RE: st: How to make a code faster - alternatives to egen var = concat(vars) ?, Date Thu, 17 Jun 2010 22:02:51 +0100

```I'll -collapse- and -merge- back again.

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

Tiago V. Pereira

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!

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```