Understanding a data step

[ari2495]

data Db_1;
set Db;
by variable_order;
if first.variable=1 then amount=0;
amount+balance;
if last.variable=1 then output;
run;

Hi, on the code as above i can't understand the use of first and last. Are they simply libraries or have they a specific function?

[Kurt_Bremser · Accepted solution]

The FIRST. and LAST. are automatic variables, created for every variable used in the BY statement. They indicate a change in the values of a variable. See this:

data have;
input x;
datalines;
1
1
1
2
2
3
;

data want;
set have;
by x;
f = first.x;
l = last.x;
run;

BTW, your data step will not work, as you use FIRST. and LAST. for a variable not included in the BY.

Also note that, for BY to work, the dataset must be sorted by the variable(s), unless the NOTSORTED option is used.