Look up and replace values from a separate table in SAS - replace

Question

Dataset HAVE includes two variables with misspelled names in them: names and friends.
Name Age Friend
Jon 11 Ann
Jon 11 Tom
Jimb 12 Egg
Joe 11 Egg
Joe 11 Anne
Joe 11 Tom
Jed 10 Ann
I have a small dataset CORRECTIONS that includes wrong_names and resolved_names.
current_names resolved_names
Jon John
Ann Anne
Jimb Jim
I need any name in names or friends in HAVE that matches a name in the wrong_names column of CORRECTIONS to get recoded to the corresponding string in resolved_name. The resulting dataset WANT should look like this:
Name Age Friend
John 11 Anne
John 11 Tom
Jim 12 Egg
Joe 11 Egg
Joe 11 Anne
Joe 11 Tom
Jed 10 Anne
In R, I could simply invoke each dataframe and vector using if_else(), but the DATA step in SAS doesn't play nicely with multiple datasets. How can I make these replacements using CORRECTIONS as a look-up table?

Answer 1

There are many ways to do a lookup in SAS.
First of all, however, I would suggest to de-duplicate your look-up table (for example, using PROC SORT and Data Step/Set/By) - deciding which duplicate to keep (if any exist).
As for the lookup task itself, for simplicity and learning I would suggest the following:
The "OLD SCHOOL" way - good for auditing inputs and outputs (it is easier to validate the results of a join when input tables are in the required order):
*** data to validate;
data have;
length name $10. age 4. friend $10.;
input name age friend;
datalines;
Jon 11 Ann
Jon 11 Tom
Jimb 12 Egg
Joe 11 Egg
Joe 11 Anne
Joe 11 Tom
Jed 10 Ann
run;
*** lookup table;
data corrections;
length current_names $10. resolved_names $10.;
input current_names resolved_names;
datalines;
Jon John
Ann Anne
Jimb Jim
run;
*** de-duplicate lookup table;
proc sort data=corrections nodupkey; by current_names; run;
proc sort data=have; by name; run;
data have_corrected;
merge have(in=a)
corrections(in=b rename=(current_names=name))
;
by name;
if a;
if b then do;
name=resolved_names;
end;
run;
The SQL way - which avoids sorting the have table:
proc sql;
create table have_corrected_sql as
select
coalesce(b.resolved_names, a.name) as name,
a.age,
a.friend
from work.have as a left join work.corrections as b
on a.name eq b.current_names
order by name;
quit;
NB the Coalesce() is used to replace missing resolved_names values (ie when there is no correction) with names from the have table
EDIT: To reflect Quentin's (CORRECT) comment that I'd missed the update to both name and friend fields.
Based on correcting the 2 fields, again many approaches but the essence is one of updating a value only IF it exists in the lookup (corrections) table. The hash object is pretty good at this, once you've understood it's declaration.
NB: any key fields in the Hash object need to be specified on a Length statement BEFOREHAND.
EDIT: as per ChrisJ's alternative to the Length statement declaration, and my reply (see below) - it would be better to state that key variables need to be defined BEFORE you declare the hash table.
data have_corrected;
keep name age friend;
length current_names $10.;
*** load valid names into hash lookup table;
if _n_=1 then do;
declare hash h(dataset: 'work.corrections');
rc = h.defineKey('current_names');
rc = h.defineData('resolved_names');
rc = h.defineDone();
end;
do until(eof);
set have(in=a) end=eof;
*** validate both name fields;
if h.find(key:name) eq 0 then
name = resolved_names;
if h.find(key:friend) eq 0 then
friend = resolved_names;
output;
end;
run;
EDIT: to answer the comments re ChrisJ's SQL/Update alternative
Basically, you need to restrict each UPDATE statement to ONLY those rows that have name values or friend values in the corrections table - this is done by adding another where clause AFTER you've specified the set var = (clause). See below.
NB. AFAIK, an SQL solution to your requirement will require MORE than 1 pass of both the base table & the lookup table.
The lookup/hash table, however, requires a single pass of the base table, a load of the lookup table and then the lookup actions themselves. You can see the performance difference in the log...
proc sql;
*** create copy of have table;
create table work.have_sql as select * from work.have;
*** correct name field;
update work.have_sql as u
set name = (select resolved_names
from work.corrections as n
where u.name=n.current_names)
where u.name in (select current_names from work.corrections)
;
*** correct friend field;
update work.have_sql as u
set friend = (select resolved_names
from work.corrections as n
where u.friend=n.current_names)
where u.friend in (select current_names from work.corrections)
;
quit;

Answer 2

Given data
*** data to validate;
data have;
length name $10. age 4. friend $10.;
input name age friend;
datalines;
Jon 11 Ann
Jon 11 Tom
Jimb 12 Egg
Joe 11 Egg
Joe 11 Anne
Joe 11 Tom
Jed 10 Ann
run;
*** lookup table;
data corrections;
length from_name $10. to_name $10.;
input from_name to_name;
datalines;
Jon John
Ann Anne
Jimb Jim
run;
One SQL alternative is to perform a existent mapping select look up on each field to be mapped. This would be counter to joining the corrections table one time for each field to be mapped.
proc sql;
create table want1 as
select
case when exists (select * from corrections where from_name=name)
then (select to_name from corrections where from_name=name)
else name
end as name
, age
, case when exists (select * from corrections where from_name=friend)
then (select to_name from corrections where from_name=friend)
else friend
end as friend
from
have
;
Another, SAS only way, to perform inline left joins is to use a custom format.
data cntlin;
set corrections;
retain fmtname '$cohen'; /* the fixer */
rename from_name=start to_name=label;
run;
proc format cntlin=cntlin;
run;
data want2;
set have;
name = put(name,$cohen.);
friend = put(friend,$cohen.);
run;

Answer 3

You can use an UPDATE in proc sql :
proc sql ;
update have a
set name = (select resolved_names b from corrections where a.name = b.current_names)
where name in(select current_names from corrections)
;
update have a
set friend = (select resolved_names b from corrections where a.friend = b.current_names)
where friend in(select current_names from corrections)
;
quit ;
Or, you could use a format :
/* Create format */
data current_fmt ;
retain fmtname 'NAMEFIX' type 'C' ;
set resolved_names ;
start = current_names ;
label = resolved_names ;
run ;
proc format cntlin=current_fmt ; run ;
/* Apply format */
data want ;
set have ;
name = put(name ,$NAMEFIX.) ;
friend = put(friend,$NAMEFIX.) ;
run ;

Answer 4

Try this:
proc sql;
create table want as
select p.name,p.age,
case
when q.current_names is null then p.friend
else q.resolved_names
end
as friend1
from
(
select
case
when b.current_names is null then a.name
else b.resolved_names
end
as name,
a.age,a.friend
from
have a
left join
corrections b
on upcase(a.name) = upcase(b.current_names)
) p
left join
corrections q
on upcase(p.friend) = upcase(q.current_names);
quit;
Output:
name age friend
John 11 Anne
Jed 10 Anne
Joe 11 Anne
Jim 12 Egg
Joe 11 Egg
Joe 11 Tom
John 11 Tom
Let me know in case of any clarifications.