laglead

SAS utilities for dynamic lead/lag value access.

%laglead()

Purpose: Creates shifted copies of variable var by looking up the value from the
same dataset at offset rows based on row numbers. Negative offset = lag,
positive offset = lead, offset=0 points to the current row.

Parameters:

  dataset=  Input dataset name (REQUIRED). Typically, specify the exact same  
            dataset as the one used in the  DATA step SET statement;  
  var=      Target variable to shift/copy (REQUIRED)  
  offset=   Integer only. Negative=lag, Positive=lead, default -1. Decimals not allowed  
  id=       Optional group ID (SINGLE variable only). When specified, the dataset  
            MUST be pre-sorted and contiguous by `id`

Assumptions & Constraints:

• offset must be an integer (no decimals)
• id supports ONLY one variable (no composite keys)
• If id is provided, the input must be sorted by id and records must be contiguous
• Row-number-based lookup: with id, shifts occur within the same id;
  without id, shifts use the physical order of the dataset
• Missing is returned when the target row does not exist

Output (naming convention):

• offset<0: &var._prev_abs(offset)
• offset>0: &var._next_abs(offset)
• offset=0: &var._next_0 (by current implementation)

Examples:

  data a;
    set sashelp.class(keep=name);
    %laglead(dataset=sashelp.class, var=name, offset=-1);
    %laglead(dataset=sashelp.class, var=name, offset=+2);
  run;

data b;
SUBJID="A";VISITNUM=1;AVAL=10;output;
SUBJID="A";VISITNUM=1;AVAL=20;output;
SUBJID="A";VISITNUM=1;AVAL=30;output;
SUBJID="A";VISITNUM=1;AVAL=40;output;
SUBJID="B";VISITNUM=1;AVAL=11;output;
SUBJID="B";VISITNUM=1;AVAL=21;output;
SUBJID="B";VISITNUM=1;AVAL=31;output;
run;

data c;
set b;
%laglead(
dataset=b
,var=AVAL
,offset= -1
,id=SUBJID
);

%laglead(
dataset=b
,var=AVAL
,offset= +1
,id=SUBJID
);
run;

version history

0.1.0(15Auguat2025): Initial version

What is SAS Packages?

The package is built on top of SAS Packages Framework(SPF) developed by Bartosz Jablonski.

For more information about the framework, see SAS Packages Framework.

You can also find more SAS Packages (SASPacs) in the SAS Packages Archive(SASPAC).

How to use SAS Packages? (quick start)

1. Set-up SAS Packages Framework

First, create a directory for your packages and assign a packages fileref to it.

filename packages "\path\to\your\packages";

Secondly, enable the SAS Packages Framework. (If you don't have SAS Packages Framework installed, follow the instruction in SPF documentation to install SAS Packages Framework.)

%include packages(SPFinit.sas)

2. Install SAS package

Install SAS package you want to use with the SPF's %installPackage() macro.

• For packages located in SAS Packages Archive(SASPAC) run:

  %installPackage(packageName)

• For packages located in PharmaForest run:

  %installPackage(packageName, mirror=PharmaForest)

• For packages located at some network location run:

  %installPackage(packageName, sourcePath=https://some/internet/location/for/packages)

  (e.g. %installPackage(ABC, sourcePath=https://github.com/SomeRepo/ABC/raw/main/))

3. Load SAS package

Load SAS package you want to use with the SPF's %loadPackage() macro.

%loadPackage(packageName)

Enjoy!