check whether variable contains specific realization

[Tim Grünebaum]

Hi all,

I would like to check (in an if environment) whether a certain value of var2 appears somewhere in var1 and consequently mark it in var3;
If possible also using a by operator to check that for specific region within var1.

Thus if there is an 8 of 5 in var1, set var3 to 1 in the specific row as can be seen below:

var1	var2	var3
0
1
2
3	8	1
4
5	10
6
7	5	1
8	11
9

I don't know if there is a simple expression or if I have to go there "by foot" with some help-variables.

Thanks
Tim

[Nick Cox]

Check out countmatch (SSC).

[Sergiy Radyakin]

generate var3=inlist(var2,5,8)

[Tim Grünebaum]

@ Nick:
Thank you. This command only counts though, but maybe I can work with it.

@ Sergiy
I don't think that will help. It's not about 5 and 8 but a variable containing specific values.

[Nick Cox]

As I understand it, countmatch does more than you want, so you just throw away what you don't want. Otherwise put, you reduce a count to an indicator.

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(var1 var2 var3)
0  . .
1  . .
2  . .
3  8 1
4  . .
5 10 .
6  . .
7  5 1
8 11 .
9  . .
end

countmatch var2 var1, gen(wanted)

list 

     +-----------------------------+
     | var1   var2   var3   wanted |
     |-----------------------------|
  1. |    0      .      .        . |
  2. |    1      .      .        . |
  3. |    2      .      .        . |
  4. |    3      8      1        1 |
  5. |    4      .      .        . |
     |-----------------------------|
  6. |    5     10      .        0 |
  7. |    6      .      .        . |
  8. |    7      5      1        1 |
  9. |    8     11      .        0 |
 10. |    9      .      .        . |
     +-----------------------------+

replace wanted = cond(wanted > 0, 1, .) 

list 

     +-----------------------------+
     | var1   var2   var3   wanted |
     |-----------------------------|
  1. |    0      .      .        . |
  2. |    1      .      .        . |
  3. |    2      .      .        . |
  4. |    3      8      1        1 |
  5. |    4      .      .        . |
     |-----------------------------|
  6. |    5     10      .        . |
  7. |    6      .      .        . |
  8. |    7      5      1        1 |
  9. |    8     11      .        . |
 10. |    9      .      .        . |
     +-----------------------------+

[Sergiy Radyakin]

Sorry, I read "Thus if there is an 8 of 5 in var1, set var3 to 1 in the specific row" as "Thus if there is an 8 or 5 in var1, set var3 to 1 in the specific row."

Perhaps there is still a typo in the original description of the task, but with your clarification it is a job for isknown.
http://www.radyakin.org/stata/isknown/

[Robert Picard]

Perhaps there's more educational benefit in showing how to solve this using merge. I tweaked the problem to add a region variable since Tim suggested that the matching could be done by region.

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(region var1 var2)
1 0  .
1 1  .
1 2  .
1 3  8
1 5 10
1 6  .
1 7  5
1 8 11
1 9  .
1 .  .
2 2  .
2 2  .
2 3  4
2 4  .
2 5  9
2 6  .
end
save "statalist_data.dta", replace

* reduce to one observation per distinct non-missing values of var1
keep region var1
bysort region var1: keep if _n == 1 & !mi(var1)

* match distinct values of var1 to values of var2
rename var1 var2
merge 1:m region var2 using "statalist_data.dta", keep(match using)

* create an indicator when values matched
gen wanted = _merge == 3

* clean up and list results
drop _merge
sort region var1
order region var1 var2 wanted
list, sepby(region)

and these are the results

. list, sepby(region)

     +-------------------------------+
     | region   var1   var2   wanted |
     |-------------------------------|
  1. |      1      0      .        0 |
  2. |      1      1      .        0 |
  3. |      1      2      .        0 |
  4. |      1      3      8        1 |
  5. |      1      5     10        0 |
  6. |      1      6      .        0 |
  7. |      1      7      5        1 |
  8. |      1      8     11        0 |
  9. |      1      9      .        0 |
 10. |      1      .      .        0 |
     |-------------------------------|
 11. |      2      2      .        0 |
 12. |      2      2      .        0 |
 13. |      2      3      4        1 |
 14. |      2      4      .        0 |
 15. |      2      5      9        0 |
 16. |      2      6      .        0 |
     +-------------------------------+