Assign first ID based on Prior ID values

[Mr_sassy_sug]

Hello Experts,

Hope all are doing fine. Please apologize to bother you with my question.

I am trying to assign the initial ID to the other ID rows based on Prior ID column. Can you please help on this to figure the way to do it.

I have

data have;
input ID $ p_id $ ;
datalines;
006 .
007 006
008 .
009 .
010 007
011 010
;
run;

I want

Here, I am trying to create the 'NEED' column with first ID number value based on P_ID. If you see row#2 has P_ID as '006' , since I have record with ID = '006' so I need to get NEED = '006' for that record. Row # 5 has P_ID = '007' which has inital P_ID is '006', so I want '006' in NEED column for rows # 5. Likewise, For Row # 6, based on all previous P_ID values, we should get NEED = '006' for that column. Can you please help on this.

Thanks all and Have a great day.

[ChrisNZ]

So you want to reference the original parent ID? And I suppose you have more than one original parent ID?

[Mr_sassy_sug]

Yes, that is correct

[Patrick]

@Mr_sassy_sug Something like below should do the job.

data have;
  input ID $ p_id $;
  datalines;
006 .
007 006
008 .
009 .
010 007
011 010
012 008
013 012
014 015
015 014
;

proc sql;
  create view hierarchy as
    select
      id as _child,
      p_id as _parent
    from have
    where p_id is not missing
    ;
quit;

%let max_depth=99;
data want(drop=_:);
  if _n_=1 then
    do;
      if 0 then set hierarchy;
      dcl hash h1(dataset:'hierarchy');
      h1.defineKey('_child');
      h1.defineData('_child','_parent');
      h1.defineDone();
    end;
  call missing(_child,_parent);

  set have;

  if not missing(p_id) then
    do; 
      _parent=p_id;
      do _i=1 to &max_depth until(h1.find(key:_parent) ne 0);
      end;
      need=_parent;
      /* investigate data if _i > &max_depth */
      if _i>&max_depth then circular_reference_flg=1;
    end;
run;

[Mr_sassy_sug]

Thank you so much, this is really helpful and it works to my situation.

Thank you so much again.

[mkeintz · Accepted solution]

If there are no circular references, then this task can be simplified:

data want;
  set have;
  if _n_=1 then do;
    declare hash h (dataset:'have (where=(not missing (p_id)))');
     h.definekey('id');
     h.definedata('p_id');
     h.definedone();
  end;
  if not missing(p_id) then do until(h.find()^=0);
    id=p_id;
  end;
  need=p_id;
  set have;
run;
    

The h.find() method for the hash object h is a way to step from ID to P_ID, then to the P_ID of the P_ID, etc., until no further P_ID can be found.  The only problem is that the loop using the h.find() method, keeps modifying  P_ID and ID until the find failure, losing the original ID and P_ID..  But this is enough to get the NEED value.

Then just re-read the original observation (via the second SET statement) to restore the original ID and P_ID values.  The point is that the two SET statement are a way to read each observation twice, once before establishing NEED, and once after.  

Additional material below:  

PS: Here's what the program would look like if you add a circularity check.  It establishes an _orig_id=id  and adds a test for "id=_orig_id" in the UNTIL clause:  

data want (drop=_:);
  set have;
  if _n_=1 then do;
    declare hash h (dataset:'have (where=(not missing (p_id)))');
     h.definekey('id');
     h.definedata('p_id');
     h.definedone();
  end;

  _orig_id=id;     /* For circularity check */

  if not missing(p_id) then do until(h.find()^=0 or id=_orig_id);
    id=p_id;
  end;
  need=p_id;
  set have;
run;

However, this code is NOT robust against having a given P_ID show up twice, when at least one instance is in a circular reference.    Although multiple instances of a given P_ID in which none of them occur is a circle does not present a problem.

[Mr_sassy_sug]

Thank you so much and this is really simple and straight to the point. I really appreciate your help.

Thanks again for your valuable on this

[Patrick]

@mkeintz This lookup will in case of a match overwrite p_id in the base table with p_id from the hash. This could lead to a wrong outcome in case of DQ issues in the base table.

[mkeintz]

---

@Patrick wrote:

@mkeintz This lookup will in case of a match overwrite p_id in the base table with p_id from the hash. This could lead to a wrong outcome in case of DQ issues in the base table.

---

Yes.  I believe that issue is addressed by the second SET statement, that follows the calculation of NEED.

"DQ issues".  Is that "Data Quality"?  I qualified my code offering as not suitable for data having circular references (although a check for circularity could be easily put in).  Is there something else I missed (won't be the first time)?