Basic question on forval loops

[John Mullahy]

For years I've used workarounds to handle the following type of problem. I've decided finally to appeal to the collective wisdom of the StataList community.

Suppose I have variables named y01, ..., y99. I wish to manipulate each in the same manner, possibly in a forval loop.

forval j=01/99 {
sum y`j'
}

does not work, as might be expected, since y01-y09 are treated as if they are named y1-y9 in the sum command.

Might anyone suggest an elegant way to handle this? The solution would ideally generalize to y001-y999, etc.

Note: Ideally I would like to avoid using

foreach z of varlist y01-y99 {

since variables other than y01-y99 might get caught in the y01-y99 varlist. But if this is the best way to proceed then so be it and I presume that something like

preserve
order ..., alpha
foreach ... {
...
}
restore

would suffice.

Thanks in advance.

[Andrew Musau]

Does it help to use the -strofreal()- function directly in the executed command?

clear
set obs 20
set seed 02112025

forval j=1/100 {
    gen year`=strofreal(`j', "%03.0f")'= rnormal()
}

forval j=1/100 {
    sum year`=strofreal(`j', "%03.0f")'
}

Res.:

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year001 |         20   -.3131233    .8361902  -2.262398   1.600142

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year002 |         20   -.2446142    1.054504   -2.07622   1.497459

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year003 |         20    .1669631    .8996776  -1.563128   1.627598

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year004 |         20   -.0029187    1.253589   -3.32213   1.362264

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year005 |         20    .1705304    1.187082  -2.977926   2.038345

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year006 |         20   -.0060827    .9878331  -1.379215   1.897073

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year007 |         20    .1206786    1.028119   -2.03441   1.801567

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year008 |         20   -.0324168     1.09227  -1.571728   2.344796

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year009 |         20    .2542958     .947083  -1.165808   2.191764

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year010 |         20    -.226149    1.065827  -2.004956    1.75305

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year011 |         20    .0607576    1.150555  -2.167209   2.340534


    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year090 |         20   -.0961276    1.141413  -2.044078   2.192554

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year091 |         20    .4514179    .8503474  -1.116466   2.571808

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year092 |         20   -.0775707    1.032296  -1.651642   2.041872

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year093 |         20   -.0283833    .8702842  -1.428963   1.786483

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year094 |         20    .4301899    1.056002  -1.230704   2.306427

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year095 |         20    .4168104    .7539987  -.7983195   1.438262

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year096 |         20    .2585093    1.148106  -1.881129   2.475704

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year097 |         20    .1610862     .719974   -1.65291   1.351457

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year098 |         20   -.1067993    .6091672  -1.522634   .7087622

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year099 |         20   -.0541567    1.058966  -1.870191   2.065479

    Variable |        Obs        Mean    Std. Dev.       Min        Max
-------------+---------------------------------------------------------
     year100 |         20    .3281591    1.037528  -1.446076   2.611331

[John Mullahy]

Thanks Andrew. This is a nice solution.

[Jeff Pitblado (StataCorp)]

How about

foreach z of varlist y?? {

[John Mullahy]

Thanks Jeff. That will certainly do the trick.

[Nick Cox]

See also earlier discussions in

SJ-21-4 pr0075 . . . . . . . . . . . . . . Speaking Stata: Loops in parallel
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q4/21 SJ 21(4):1047--1064 (no commands)
tutorial discussing looping in parallel using foreach
and forvalues

https://journals.sagepub.com/doi/pdf...6867X211063415

(Section 2 discusses again how to insert leading zeros)

SJ-21-2 pr0074_1 . . . . . . Erratum: Speaking Stata: Loops, again and again
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q2/21 SJ 21(2):555 (no commands)
erratum for a line of code

https://journals.sagepub.com/doi/pdf...6867X211025839

SJ-20-4 pr0074 . . . . . . . . . . . . Speaking Stata: Loops, again and again
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . N. J. Cox
Q4/20 SJ 20(4):999--1015 (no commands)
provides updated guidance on using foreach and forvalues for
looping through lists of values and repeating commands using
members of those lists in turn

(basic tutorial)
https://journals.sagepub.com/doi/pdf...36867X20976340

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

https://journals.sagepub.com/doi/pdf...867X1001000115

(a solution similar to that of Andrew Musau)

[Evgeny Saburov]

I also often find myself needing to loop over variables that have a particular pattern in their names, but -ds- and varlist wildcards such as "??" don't always cut it. So I turn to regex:

clear all

gen y01 = .
gen y02 = .
gen y03 = .
gen y04 = .
gen yy05 = .
gen x05y = .
gen y04a = .

foreach var of varlist _all {
    if regexm("`var'", "^y[0-9]+$") {
        disp "variable `var' - matched regex"
        sum `var'
    }
}

[Hemanshu Kumar]

Evgeny Saburov I don't quite follow.

In your example, if I just do

. sum y??

    Variable |        Obs        Mean    Std. dev.       Min        Max
-------------+---------------------------------------------------------
         y01 |          0
         y02 |          0
         y03 |          0
         y04 |          0

which are the same variables your regex matched. Could you give a better example?

[Evgeny Saburov]

Hemanshu Kumar

I should have used a better example of variables that would match with "??" but not with regex. For example something like "ya4" would also match with y??, perhaps unintentionally, if we were only interested in variables that start with "y" and end with an arbitrary number of digits. My point is that it's just easier and safer to define an accurate pattern of variable names that are of interest with regex.

[Yankuba Jarjusey]

Hello guys.
I am new to Stata. I am trying to replace "I don't know" with "0", but the replacement is not working. What am I missing here? I need your help.
Manually, I cannot replace all these options with "0" because I have over 1000 observations in the dataset.

[Clyde Schechter]

There is very little chance you will get a timely and helpful reply to this post. You have placed it at the end of a thread that it is entirely unrelated to. So somebody who might be interested in answering a question like this one will never know it's even here. You don't show any example data, so nobody but you knows what kind of variable you are working with: it matters greatly, as different solutions would apply to different kinds of variables. And, finally, you said that "the replacement is not working." But what does that mean? There are many ways in which a command fails to work: did it crash your computer, cause Stata to close, give you an error message, none of the preceding but produced output or changes to your data that you didn't expect? And what specific command is the "replacement" you attempted?

So, in short, you have given almost no information about your problem and posted it in a place where the most helpful people are unlikely to see it. To get help, I recommend:

1. Do the post over, starting a new thread, and give that thread a title that says what the question is about.
2. Show example data, using the -dataex- command to do that. If you are running version 16 or later, or a fully updated version 15.1 or 14.2, -dataex- is already part of your official Stata installation. If not, run -ssc install dataex- to get it. Either way, run -help dataex- to read the simple instructions for using it. -dataex- will save you time; it is easier and quicker than typing out tables. It includes complete information about aspects of the data that are often critical to answering your question but cannot be seen from tabular displays or screenshots. It also makes it possible for those who want to help you to create a faithful representation of your example to try out their code, which in turn makes it more likely that their answer will actually work in your data.
3. Show the exact command you tried, and show any output or messages that Stata gave in the Results window. If there was no message or output, then explain what Stata actually did. If Stata did do something to the variable, but it was not what you expected, show what the variable looked like after the command was run: probably it's easiest to do that by running -dataex- again, but perhaps -list- will do the trick.

More generally, I recommend you read the Forum FAQ for lots of helpful tips on how to ask questions effectively, ensuring your best chance of getting a useful reply. You can access the FAQ by clicking on the "FAQ" button that you will find just below the Statalist banner at the top of the page.

[Yankuba Jarjusey]

Thank you for helping me to better frame the question.
The variable is a string (str) with non-numeric characters: "Yes," "No," and "I don't know." I am assessing respondents' knowledge of hepatitis B virus curability, and the possible responses are "Yes," "No," and "I don't know."
The responses "No" or "I don't know" should be scored "0." I received no red error message in the output window, but those characters were not replaced with "0."

command in Stata 18, "replace Q2= "0" if Q2=="No" | Q2=="I don't know". All the "No" were replaced, but not the "I don't know" responses.
In the output window/panel, below the command lines, it says "0 real changes made," and I confirmed this by tabulating the variable containing such responses. The responses were still the same because they were not replaced with the "0s" I wanted.

I hope I have provided enough information to better describe the issue I am facing now. I appreciate your swift response, Mr. Schechter.

[Joseph Coveney]

I appreciate your swift response, Mr. Schechter.

Try looking for responses on this thread.

[Yankuba Jarjusey]

Thanks Joseph.