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# Re: st: Loop to replace values of a variable

 From Jeph Herrin To statalist@hsphsun2.harvard.edu Subject Re: st: Loop to replace values of a variable Date Wed, 18 Dec 2013 14:00:27 -0500

```Good point. So

sort n
replace x=x[1] + _n*.1

will do.

On 12/18/2013 11:22 AM, Nick Cox wrote:
```
```In principle, yes. In practice, this means repeated addition of 0.1;
but 0.1 is a good example of a decimal that looks simple but can't be
held exactly as a binary. Do something like this

set obs 100
gen y1 = 0
replace y1 = y[_n-1] + 0.1 in 2/L
gen y2 = (_n-1)/10
edit y?

to convince yourself that the second method gives a better
approximation than the first.

More discussion at

SJ-10-1 pr0051  . . . . . . . . . . . . Stata tip 85: Looping over nonintegers
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
Q1/10   SJ 10(1):160--163                                (no commands)
tip on using forvalues to loop over numbers

http://www.stata-journal.com/sjpdf.html?articlenum=pr0051

Nick
njcoxstata@gmail.com

On 18 December 2013 14:34, Jeph Herrin <stata@spandrel.net> wrote:
```
```A solution that doesn't require knowing the value of x[1] in advance:

sort x
replace x=x[_n-1]+0.1 if _n>1

hth,
Jeph

On 12/18/2013 9:04 AM, emanuele mazzini wrote:
```
```
Yes, the way Marteen suggested worked greatly.
Thank you!!

2013/12/18 Fabrizio Colella - 1348010 <colella.fabrizio@studbocconi.it>:
```
```
you generated x as Marteen suggested, now you just have to subtract:

gen x = _n*.1
gen y = -2.6+x

Fabrizio

----- Messaggio originale -----
Da: "Nick Cox" <njcoxstata@gmail.com>
A: statalist@hsphsun2.harvard.edu
Sent: Mercoledì, 18 dicembre 2013 14:49:34
Oggetto: Re: st: Loop to replace values of a variable

For -2.5(0.1)2.1 or -2.5(0.1)2.5, you can still divide integers by 10.
No loop needed as _n always gives you integers in sequence.

Nick
njcoxstata@gmail.com

On 18 December 2013 13:44, emanuele mazzini <madsoenistata@gmail.com>
wrote:
```
```
Oh, yes, I see. Thank you very much for your answers, but I may have
oversimplified, since what you said would fit in this case, as x is
exactly = _n/10, but my problem is slightly more complex.

What if the values I want to replace go from -2.5 to 2.15, still with
a 0.1 interval? In this case I'd still need a loop, right?

2013/12/18 Maarten Buis <maartenlbuis@gmail.com>:
```
```
no need to loop:

gen x = _n*.1

Hope this helps,
Maarten

On Wed, Dec 18, 2013 at 2:33 PM, emanuele mazzini
```
```
Dear all statalist users,

I would like to program a (relatively) simple loop to replace the
values of a variable I created, but I cannot  figure it out how to
write the syntax.

The structure of my data is very simple:
I have 300 observations and a variable, say x, that in the first cell
(i.e. for n=1) is equal to 0.1, while it is missing for all other 299
cells. Data look like:

n     x
1    0.1
2     .
3     .
4     .
.
.
.
.
.
299  .
300  .

I would like the loop to replace the missing values of my variable by
going from cell 2 to cell 300, and to have a replace that would be at
a 0.1 intervals, so as to obtain data that look like:

n     x
1    0.1
2    0.2
3    0.3
4    0.4
.
.
.
.
.
299  29.9
300  30

I can obviously do it by hand, but a loop would be naturally much more
efficient!
Does anyone know how to make it?
```
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