seq number issue

[pavank]

data ds;
set sashelp.class;
if mod(_n_,2)=1 then seq=1;output;
else  mod(_n_,2)=0 then seq=1+1;

    output;
keep name seq;
proc print noobs;
run;

required output
Name Seq
Alfred 1
Alice 1
Alice 1
Barbara 2
Carol 2
Carol 2
Henry 3
James 3
James 3
Jane 4
Janet 4
Janet 4
Jeffrey 5
John 5
John 5
Joyce 6
Judy 6
Judy 6
Louise 7
Mary 7
Mary 7
Philip 8
Robert 8
Robert 8
Ronald 9
Thomas 9
Thomas 9
William 10

[Astounding · Accepted solution]

Making reasonable assumptions about what the input looks like, here's what I came up wth:

data want;
   set have;
   if mod(_n_, 2) then do;  
      seq + 1;
      output;
   end;
   else do;
      output;
      output;
   end;
run;

So you are usig a lot of the right tools, but definitely need to tweak the program to get the desired result.

[PaigeMiller]

Could you explain the desired output? It appears that you want Alfred once, Alice twice, Barbara once, Carol twice, and so on. What is the logic?

[mkeintz]

I see you already have a solution.  Here's is an alternative that eschews DO groups:

data want;
  set have;
  seq+mod(_n_,2);
  output;
  if mod(_n_,2)=0 then output;
run;