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Is it possible to perform a merge where key values are split across two columns?

Normally when performing a horizontal join of datasets, or performing a lookup, the key values exist in a single column, however sometimes 'dirty' data may appear in different forms, and in different columns.

Submit the following code to generate a sample dataset and a lookup table:

*** Generate some test data which may have one field, or the other, or both *** ;
data ds1 (drop = gender)
     ds2 (drop = sex)
  set sashelp.class (keep = name sex) ;
    if (sex = 'M' and ranuni(0) > 0.6) then 
      do ;
        gender = '1' ;
        if ranuni(0) > 0.4 then sex = '' ;
      end ;
	if (sex = 'F' and ranuni(0) > 0.7) then 
      do ;
        gender = '2' ;
	if ranuni(0) > 0.4 then  sex = '' ;
      end ;
run ;

data ds3 ;
  merge ds1 ds2 ;
    by name ;
run ;

*** Generate a lookup table with all data values *** ;
data gen_lookup ;
  gen_sex = 'F' ;
  gen_type = 'Female' ;
  output ;
  gen_sex = '2' ;
  gen_type = 'Female' ;
  output ;
  gen_sex = 'M' ;
  gen_type = 'Male' ;
  output ;
  gen_sex = '1' ;
  gen_type = 'Male' ;
  output ;
run ;


Name       Sex    gender

Alfred      M       1
Alice               2
Barbara     F
Carol       F
Henry       M       1
James       M
Jane        F
Janet       F
Jeffrey     M
John        M       1
Joyce       F
Judy        F
Louise      F
Mary        F       2
Philip      M
Robert              1
Ronald      M
Thomas              1
William     M

There are two columns containing the 'key' values - sex and gender. In the generated dataset values may in appear in one, or the other, or both columns.  Although values differ, the relationship remains constant:

M = 1 = Male

F = 2 = Female

In order to perform the lookup, the key value is the first non-missing value from either sex or gender.

While it would be possible to consolidate this data into a single column, this would require a further pass through the data, and create an inefficiency.

To perform the lookup on the 'best' value, simply use the COALESCE function on the join condition in an SQL clause:

*** Join the lookup table by a combination of the sex and gender columns *** ;
proc sql ;
  create table ds4 as
  select  ds3.*
  from  ds3
  where coalesce(gender, sex) = gen_sex
quit ;

The COALESCE function returns the first non-missing value from a list of arguments, and produces the desired result:

Name       Sex    gender    gen_type

Alfred      M                Male
Alice               2        Female
Barbara     F                Female
Carol       F                Female
Henry               1        Male
James               1        Male
Jane        F                Female
Janet       F                Female
Jeffrey     M       1        Male
John                1        Male
Joyce       F                Female
Judy                2        Female
Louise      F                Female
Mary        F       2        Female
Philip              1        Male
Robert      M                Male
Ronald              1        Male
Thomas              1        Male
William             1        Male
Alan D Rudland
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