In a previous question, I got an efficient solution to generate a variable and at the same time order it:
sysuse auto, clear
generate random = runiform(), before(make)
This solution does not seem to work if the egen command is used:
egen avgprice = mean(price), before(make)
option before() not allowed
r(198);
Is it possible to generate a variable and at the same time order it when using egen?
The egen command does not have an option similar to the before() option of generate.
However, you can accomplish what you want by writing a small program:
program define egen2
unab allvars : *
gettoken firstvar : allvars
tempname var
gettoken firstarg 0 : 0, parse("=")
egen `var' `0'
generate `firstarg' = `var', before(`firstvar')
end
You could then do the following:
sysuse auto, clear
egen2 foo = mean(price)
EDIT:
The program can be reduced to the following if you do not want to completely avoid order:
program define egen2
gettoken firstarg 0 : 0, parse("=")
egen `firstarg' `0'
order `firstarg'
end
Related
I am trying to create a school-level learning inequality index based on the difference in learning outcomes between the top 10% and the bottom 50% of students in each school. The data are student-level (below is my attempt) but evidently, I am not creating the deciles at the school level. I imagine I need to use a foreach loop, but that is not yet something I know am fluent at.
My attempt:
bysort IDSCHOOL: egen pv__std_deciles = std(avg_pv)
xtile pv_deciles=avg_pv, nq(10)
bysort IDSCHOOL: egen school_pv_5 = mean(avg_pv) if pv_deciles<6
bysort IDSCHOOL: egen school_pv_10 = mean(avg_pv) if pv_deciles==10
egen max_sp_10=max(school_pv_10), by(IDSCHOOL)
egen max_sp_5=max(school_pv_5), by(IDSCHOOL)
gen school_pv_diff= max_sp_10 - max_sp_5
sort IDSCHOOL
quietly by IDSCHOOL: gen dup = cond(_N == 1, 0, _n)
drop if dup > 1
isid IDSCHOOL
In Stata I am trying to repeat code inside an if qualifier using perhaps a forvalues loop. My code looks something like this:
gen y=0
replace y=1 if x_1==1 & x_2==1 & x_3==1 & x_4==1
Instead of writing the & x_i==1 statement every time for each variable, I want to do it using a loop, something like this:
gen y=0
replace y=1 if forvalues i=1/4{x_`i'==1 &}
LATER EDIT:
Would it be possible to create a local in the line of this with the elements added together:
forvalues i=1/4{
local text_`i' "x_`i'==1 &"
display "`text_`i''"
}
And then call it at the if qualifier ?
Although you use the term "if statement" all your code is phrased in terms of if qualifiers, which aren't commands or statements. (Your use of the term "statement" is looser than customary, but that doesn't affect an answer directly.)
You can't insert loops in if qualifiers.
See for the differences
help if
help ifcmd
The entire example
gen y = 0
replace y = 1 if x==1 | x==2 | x==3 | x==4
would be better as
gen y = inlist(x, 1, 2, 3, 4)
or (dependent possibly on whatever values are allowed)
gen y = inrange(x, 1, 4)
A loop solution could be
gen y = 0
quietly forval i = 1/4 {
replace y = 1 if x == `i'
}
We can't discuss whether inlist() or inrange() would or would not be a solution for your real problem if you don't show to us.
I usually don't like - in Nick's terms - to write code to write code. I see an immediate, though not elegant nor 'heterodox', solution to your issue. The whole thing amounts to generate an indicator function for all your indicators, and use it with your if qualifier.
Implicit assumptions, which make this a bad, non-generalizable solution, are: 1) all variables are dummies, and you need them to be == 1, and 2) variable names are conveniently ordered 1 to N (although, if that is not the case, you can easily change the forv into a 'foreach var of varlist etc.')
g touse = 1
forv i =1/30{
replace touse = touse * x_'i'
}
<your action> if touse == 1
I have a dataset with multiple subgroups (variable economist) and dates (variable temps99).
I want to run a tabsplit command that does not accept bysort or by prefixes. So I created a macro to apply my tabsplit command to each of my subgroups within my data.
For example:
levelsof economist, local(liste)
foreach gars of local liste {
display "`gars'"
tabsplit SubjectCategory if economist=="`gars'", p(;) sort
return list
replace nbcateco = r(r) if economist == "`gars'"
}
For each subgroup, Stata runs the tabsplit command and I use the variable nbcateco to store count results.
I did the same for the date so I can have the evolution of r(r) over time:
levelsof temps99, local(liste23)
foreach time of local liste23 {
display "`time'"
tabsplit SubjectCategory if temps99 == "`time'", p(;) sort
return list
replace nbcattime = r(r) if temps99 == "`time'"
}
Now I want to do it on each subgroups economist by date temps99. I tried multiple combination but I am not very good with macros (yet?).
What I want is to be able to have my r(r) for each of my subgroups over time.
Here's a solution that shows how to calculate the number of distinct publication categories within each by-group. This uses runby (from SSC). runby loops over each by-group, each time replacing the data in memory with the data from the current by-group. For each by-group, the commands contained in the user's program are executed. Whatever is left in memory when the user's program terminates is considered results and accumulates. Once all the groups have been processed, these results replace the data in memory.
I used the verbose option because I wanted to present the results for each by-group using nice formatting. The derivation of the list of distinct categories is done by splitting each list, converting to a long layout, and reducing to one observation per distinct value. The distinct_categories program generates one variable that contains the final count of distinct categories for the by-group.
* create a demontration dataset
* ------------------------------------------------------------------------------
clear all
set seed 12345
* Example generated by -dataex-. To install: ssc install dataex
clear
input str19 economist
"Carmen M. Reinhart"
"Janet Currie"
"Asli Demirguc-Kunt"
"Esther Duflo"
"Marianne Bertrand"
"Claudia Goldin"
"Bronwyn Hughes Hall"
"Serena Ng"
"Anne Case"
"Valerie Ann Ramey"
end
expand 20
bysort economist: gen temps99 = 1998 + _n
gen pubs = runiformint(1,10)
expand pubs
sort economist temps99
gen pubid = _n
local nep NEP-AGR NEP-CBA NEP-COM NEP-DEV NEP-DGE NEP-ECM NEP-EEC NEP-ENE ///
NEP-ENV NEP-HIS NEP-INO NEP-INT NEP-LAB NEP-MAC NEP-MIC NEP-MON ///
NEP-PBE NEP-TRA NEP-URE
gen SubjectCategory = ""
forvalues i=1/19 {
replace SubjectCategory = SubjectCategory + " " + word("`nep'",`i') ///
if runiform() < .1
}
replace SubjectCategory = subinstr(trim(SubjectCategory)," ",";",.)
leftalign // from SSC
* ------------------------------------------------------------------------------
program distinct_categories
dis _n _n _dup(80) "-"
dis as txt "fille = " as res economist[1] as txt _col(68) " temps = " as res temps99[1]
// if there are no subjects for the group, exit now to avoid a no obs error
qui count if !mi(trim(SubjectCategory))
if r(N) == 0 exit
// split categories, reshape to a long layout, and reduce to unique values
preserve
keep pubid SubjectCategory
quietly {
split SubjectCategory, parse(;) gen(cat)
reshape long cat, i(pubid)
bysort cat: keep if _n == 1
drop if mi(cat)
}
// show results and generate the wanted variable
list cat
local distinct = _N
dis _n as txt "distinct = " as res `distinct'
restore
gen wanted = `distinct'
end
runby distinct_categories, by(economist temps99) verbose
This is an example of the XY problem, I think. See http://xyproblem.info/
tabsplit is a command in the package tab_chi from SSC. I have no negative feelings about it, as I wrote it, but it seems quite unnecessary here.
You want to count categories in a string variable: semi-colons are your separators. So count semi-colons and add 1.
local SC SubjectCategory
gen NCategory = 1 + length(`SC') - length(subinstr(`SC', ";", "", .))
Then (e.g.) table or tabstat will let you explore further by groups of interest.
To see the counting idea, consider 3 categories with 2 semi-colons.
. display length("frog;toad;newt")
14
. display length(subinstr("frog;toad;newt", ";", "", .))
12
If we replace each semi-colon with an empty string, the change in length is the number of semi-colons deleted. Note that we don't have to change the variable to do this. Then add 1. See also this paper.
That said, a way to extend your approach might be
egen class = group(economist temps99), label
su class, meanonly
local nclass = r(N)
gen result = .
forval i = 1/`nclass' {
di "`: label (class) `i''"
tabsplit SubjectCategory if class == `i', p(;) sort
return list
replace result = r(r) if class == `i'
}
Using statsby would be even better. See also this FAQ.
I am having a problem calling maximization options in a user-defined program. For example, the following works perfectly:
sysuse nlsw88, clear
probit collgrad age grade, tech(bfgs)
But, when I define a function that calls on Probit, I get an error message of "option tech() not allowed". Here's the code for that
program probit_test, eclass
version 10.1
if replay() {
syntax [anything] [, Level(real 95) ]
eret di, level(`level')
}
else {
qui {
syntax [varlist] [if] [in], [Level(real 95) *]
tempvar touse e1
tempname beta var
mark `touse' `if' `in'
markout `touse'
gettoken depv vl:varlist
probit `depv' `vl' if `touse', tech(bfgs)
g `e1'=e(sample)
loc N=r(N)
matrix `beta'=e(b)
matrix `var'=e(V)
ereturn post `beta' `var', dep(`depv') e(`e1') obs(`N')
cap drop _d*
}
eret di, level(`level')
}
end
****
sysuse nlsw88, clear
probit_test collgrad age grade
Edit: I just wanted to add that this is not the actual program I am running, but a simple version that shows the problem.
Your probit_test program is telling Stata to behave as if it was version 10.1. In 10.1, the Broyden–Fletcher–Goldfarb–Shanno algorithm was not yet available, so it errors. Change the version to something more current (bfgs was introduced in v11), and it should run fine.
I am trying to create a variable for each year in my data based on mathematical expressions of other variables (I have annual data and used "..." to avoid writing each year). I am using the summarize command in Stata to extract the standard deviation but Stata does not recognize the frac variable. I have tried to use egen but that results in an unknown function error. Using gen results in an already defined variable. I would appreciate anyone helping with the following code or pointing me to a link where this issue has been discussed.
foreach yr of numlist 1995...2012 {
local row = `yr' - 1994
local numerator = 100*(income - L1.income)
local denominator = ((abs(income) + abs(L1.income)) / 2)
local frac = (`numerator' / `denominator')
summarize frac
local sdfrac = r(sd)
matrix C[`row', 1] = `numerator'
matrix C[`row', 2] = `denominator'
matrix C[`row', 3] = `sdfrac'
}
If I am understanding your question right, maybe you don't need to use a loop until the end and then you can post the results to a postfile:
This is just a thought:
tempname memhold
tempfile filename
postfile `memhold' year sdfrac using `filename'
gen row=year-1994
gen numerator=100*(income-L1.income)
gen denominator=((abs(income)+abs(L1.income))/2)
gen frac=numerator/denominator
foreach yr of numlist 1995...2012 {
summarize frac if year=`yr'
local sdfrac=r(sd)
post `memhold' (year) (`sdfrac')
}
postclose `memhold'
clear all
use `filename'
*View Results
list
This code should get you a data set with the name of the year and the standard deviation of the frac variable as variables.
In a comment, OP added a question about code similar to this (but ignored the request to post it in a more civilised form). Note that backticks or left quotation marks in Stata clash with SO mark-up codes in comments. Presumably some
tempname memhold
definition preceded this.
postfile `memhold' year sdfrac sex race using myresults
levels of sex, local (s)
levelsof race, local (r)
foreach a of local s {
foreach b of local r {
forval yr = 1995/2012 {
summarize frac if year == `yr' & sex == `a' & race == `b'
post `memhold' (`yr') (`r(sd)') (`sex') (`race')
}
}
}
Let's focus on what the problem is. You want the standard deviations of frac for all combinations of sex, race and year in a separate file. That's one line
collapse (sd) frac, by(year sex race)
If you want to see a table alongside the data, consider
egen group = group(sex race year), label
and then
tab group, su(frac)
or
tabstat frac, by(group) stat(sd)
This code modifies that by #Pcarlitz, mostly by simplifying it. I can't check with your data, which I don't have.
It's too long to fit into a comment.
I would not use a temporary file as you want to save these results, it seems.
tempname memhold
postfile `memhold' year sdfrac using myresults
gen frac = (100*(income - L1.income))/((abs(income) + abs(L1.income))/2)
forval yr = 1995/2012 {
summarize frac if year==`yr'
post `memhold' (`yr') (`r(sd)')
}
postclose `memhold'
use myresults
list
UPDATE As in a later answer, consider collapse as a much simpler direct alternative here.