LagLead Macro

UPDATE: If you have SAS/ETS installed, you can use proc expand as an alternative. There are a ton of options with this procedure but here is the syntax to emulate the below code:

proc expand data = sashelp.class out = example method = none ;
  convert age = sumage / transform = ( cmovsum 5 trimleft 2 trimright 2 ) ;
run ;

The SAS supplied LAG() function is used to retain previously read variables. There is no supplied LEAD function so the below lagLead function was created.

The key to making this work is to LINK to a DO LOOP that utilizes the POINT= option on the SET statement to read the data in random access mode. A RENAME= option was required to not overwrite the existing VAR of interest in the program data vector (PDV).

In the below example, while sitting on row 5 the prior two, current row and next two rows are summed resulting in a value of 65 ( 13 + 14 + 14 + 12 + 12 ).

/**************************************************************************
*     Program: lagLead.sas
*      Author: Tom Bellmer
*     Created: 05NOV2014 
*     Purpose: read and sum X rows before and after current row
**************************************************************************/

%macro lagLead( 
    dsn      = sashelp.class
  , outdsn   = example
  , var      = age
  , outvar   = sumage
  , lag      = 2
  , lead     = 2 
) ;

  %local tempvar ;
  %let tempvar = temp_%sysfunc(ceil( %sysfunc( ranuni(0) ) * 10000 ) ) ;

  data &outdsn.( drop = &tempvar. ) ;
    set &dsn. nobs = totalrows ;
      if _n_ > &lag. and _n_ <= ( totalrows - &lead. ) then link laglead ;
      output ;
    return ;

    laglead:
      do i = ( _n_ - &lag. ) to ( _n_ + &lead. ) ;
        set &dsn.( keep = &var. rename = ( &var. = &tempvar. ) ) point = i ;
        &outvar. = sum( &outvar., &tempvar. ) ;
      end ;
    return ;
  run ;
%mend ;

/* EOF: lagLead.sas  */