Logical variables in SAS

Logical variables:

We are working based on 2 variables

1. First.Variable
2. Last.variable

• If First. variable is 1, then we will get first occurrence.
• If First. variable is 0, then we will get remaining occurrence except first occurrence.
• If Last. variable is 1, then we will get last occurrence.
• If last. variable is 0, then we will get except last occurrence include first occurrence.

/* To report first occurrence information */ Ex: Data medi; Input Gid $drug$ sdate edate ; Informat   sdate edate  date9. Format sdate edate date 9; Cards; G₁₀₀   col5mg    12jan2006   16jan2006 G₁₀₁  col5mg    13jan2006   17jan2006 G₁₀₂  col5mg    13jan2006   17jan2006 G₁₀₁   col10mg    21jan2006   25jan2006 G₁₀₂   col5mg      23jan2006   27jan2006 G₁₀₀   col10mg    23jan2006   29jan2006 G₁₀₀   col15mg    01feb2006   05feb2006 G₁₀₁   col10mg    03feb2006   07feb2006 G₁₀₂   col15mg    03feb2006   06feb2006 G₁₀₃   col10mg    03feb2006   04feb2006 ; Proc sort data = medi; By Gid; Run; Proc print data =medi; Run; Data first; Set medi; By Gid; If first .gid =1; Run; Proc print data =first; Run;

/* To report remaining occurrence except first to report each and every patient except first visit information*/

Ex; Data remain1; Set medi; By gid; If first.gid=0; Run; Proc print data=remain1; Run;

/* To report last occurrence –subject of each patients last visiting information*/

Ex: Data last; Set medi; By gid; If last.gid=1; Run; Proc print data=last; Run;

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/* To report each and every patients visiting information except last visit information*/

Ex; Data remain2; Set medi; By gid; If last.gid=0; Run; Proc print data=remain2; Run;

/* To report first and last occurrence information*/

Ex; Data firstlast Set medi; By gid; If first.gid=1 or last.gid =1; Run; Proc print data=firstlast; Run;

/* To report which group visited only once*/

Ex; Data flast; Set medi; By gid; If first.gid=1 and last.gid=1; Run; Proc print data=flast; Run;

/* To report remaining occurrence except first and last*/

Ex; Data remain3; Set medi; By gid; If first.gid=0 and last.gid=0; Run; Proc print data=remain3; Run;  

Retain statement:

        It can be used to calculate running total or cumulative tools.

• Using retain statement, we can reassign required variables current data value.
• If we omit 0, it default stores dot(.).

Ex: Data market; Input month $sale; Cards; Jan 200 Feb 300 Mar . Apr 400 May 500 June 200 ; Data market 1; Set market; Retain total 0; Total = sum (total, sale); Run; Proc print data = market1; Run; To generate the output window with out using any procedure application(use with data set block) Ex; Data _null_; Set market; File print; Put month sale; Run;  

Null data set creation:

(with variable and with out observations) using with data set block /* To delete required observations from existed data set*/ Ex: Data market ; Set market; If sale < 400 then delete; Run;

• If we run delete statement without any condition it delete overall data from existing data set.

Ex: Data market1 ; Set market; delete; Run; Ex: Data market1 ; Set market; If sale >=400 ; Run;

/* null data set creation */

Ex: Data demo; Length pid 4 age 3 Race $ 6; delete; Run;

• -Null-, without data set creation.
• Null data set, with variables and with out observations.

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