SAS - Using the retain statement

I have a dataset with ids, dates and amounts. Each id may have a few rows depending on the transaction amounts and the number of transactions performed. I need to use a retain statement t开发者_如何转开发o find the difference in time between the first change in amount. I know I need to retain all 3 variables but am unsure how to go about this? Any help would be great

Here's a basic use of a retain statement. I can't tell exactly what you need from your description. Maybe you need to retain a second variable and then use if ... then ... else ... (dates match, then ...., else....) Anyway, maybe this will get you started...

 DATA in;
    INPUT id var1 ;
    DATALINES;
      1  12   
      1  24   
      1  26   
      2  20   
      2  25   
      2  11  
 ;

 DATA out (drop=var1_lag);
   set in; 
   by id; 
   if first.id then diff=.;
   else             diff = var1 - var1_lag;
   var1_lag = var1;
   retain var1_lag;

 PROC PRINT data=out; 
 RUN; 

Output:

 Obs    id    var1    diff

  1      1     12        .
  2      1     24       12
  3      1     26        2
  4      2     20        .
  5      2     25        5
  6      2     11      -14