(Beginner SAS) How to do double for loop to generate keep list?

[RogerJones]

I have a very large dataset with over 1000 columns, with column names formatted like this:

WORLDDATA.table2_usa_2017_population
WORLDDATA.table2_japan_2017_gnp

I only need to keep a subset of these parameters for a select few countries. I specify the custom lists:

%let list1 = usa canada uk japan southafrica;
%let list2 = population crimerate gnp;

How do I do a double for loop like so:

  param_list = []
  for (i in list1) {
    for (j in list2) {
      param_name = WORLDDATA.table2_{list1[i]}_2017_{list2[j]}
      param_list.append(param_name)
    }
  }

such that I can use param_list in

data final_dataset;
  set WORLDDATA.table2;
  keep {param_list};
run;

Thank you!

[Reeza]

If you know the variables and the naming structure is pretty fixed you have a few options that I see:

1. Generate a dynamic list using a macro approach

2. Select the names using pattern matching from the list, assumed fixed pattern of table2_COUNTRY_YEAR_STATISTIC. Use SCAN() to extract those portion of the name. 

3. Reformat the data such that it's in a long/longer format and then filter/manipulate it. 

For the long run, I suspect #3 is better because the countries will be rows rather than in the variable name. 

Approach #2 - note the index (2/4) may be wrong, you should test this.

proc sql noprint;
select name into :name_list separated by " "
from sashelp.vcolumn where memname = 'WORLDDATA'
and lower(scan(name, 2, "_.")) in ('use', 'canada', 'japan')
and lower(scan(name, 4, "_.")) in ('population', 'crimerate', 'gap');
quit;

%put &name_list.;

data want;
set worldData;
keep &name_list;
run;

For an example of #3 I'd need more information on the sample structure. 

---

@RogerJones wrote:

I have a very large dataset with over 1000 columns, with column names formatted like this:

WORLDDATA.table2_usa_2017_population
WORLDDATA.table2_japan_2017_gnp

I only need to keep a subset of these parameters for a select few countries. I specify the custom lists:

%let list1 = usa canada uk japan southafrica;
%let list2 = population crimerate gnp;

How do I do a double for loop like so:

  param_list = []
  for (i in list1) {
    for (j in list2) {
      param_name = WORLDDATA.table2_{list1[i]}_2017_{list2[j]}
      param_list.append(param_name)
    }
  }

such that I can use param_list in

data final_dataset;
  set WORLDDATA.table2;
  keep {param_list};
run;

Thank you!

---

[PGStats]

I like Approach #2 best, and would write it:

proc sql noprint;
select name into :name_list separated by " "
from sashelp.vcolumn 
where memname = 'WORLDDATA' and prxmatch("/_(usa|canada|uk|japan|southafrica)_2017_(population|crimerate|gnp)/i", name);
quit;

%put &name_list.;

data want;
set worldData(keep=&name_list.);
run;

[Astounding]

I think you are seeking something more generic, along the lines of a macro:

%macro vlist (list1=, list2=) ;
%local j k ;
%do j=1 %to %sysfunc(countw(&list1) ) ;
%do k=1 %to %sysfunc(countw(&list2) ) ;
table2_%scan(&list1, &j)_2017_%scan(&list2, &k)
%end;
%end;

%mend vlist;

Then you can use the macro where you want the list of names such as:

drop %vlist (list1= usa canada uk japan southafrica,
list2 = population crime rate gnp) ;