# Re: st: making new variables for each obs

 From Ulrich Kohler <[email protected]> To [email protected] Subject Re: st: making new variables for each obs Date Tue, 25 Jan 2005 15:40:39 +0100

```��모(Byungmo Kim) wrote:
> In my dataset,
> each observaion has 23 variables ( year  name  fiscalyear  v1  v2  v3
> .........  v20 )
>
> I'd like to make vars of standard deviation of sequential 10 variables.
>
> in other words,
>
>            new variables ----------- standard deviation of 10 variables  (
> for v1 to v10 )  -->   std1 standard deviation of 10 variables  ( for v2 to
> v11 ) -->    std2 standard deviation of 10 variables  ( for v3 to v12 ) -->
>    std3 .
>     .
>     .
>     .
>    standard deviation of 10 variables  ( for v11 to v20 ) -->  std11
>
> how can i do this?? please teach me ..
> i'm very new to stata.

One way to do this would be

. egen std1to10 = rstd(v1-v10)
. egen std2to11 = rstd(v2-v11)
...
etc

which requires that your variables are in the right order. (You may change the
order of variables with -order-)

You may also put this in a loop, to save some typing. There are several ways
to do this, but one is:

. forv i = 1/14 {
.	local j = `i' + 9
.	egen std`i'to`j' = rstd(v`i'-v`j')
.}

And, finally: For problems like that it is often better to change the data
structure from wide to long, and to work with -by varlist:-. However this
would require some more teaching. To start with, take a look at

. h reshape

Also note the excellent introduction in the Stata Journal article by Cox:

SJ-2-1  pr0004  . . . . . . . . . . Speaking Stata:  How to move step by: step
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
Q1/02   SJ 2(1):86-102                                   (no commands)
explains the use of the by varlist : construct to tackle
a variety of problems with group structure, ranging from
simple calculations for each of several groups to more
advanced manipulations that use the built-in _n and _N

regards
uli

--
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```