Change values with same value

[BrahmanandaRao]

data dss;
set sashelp.class;
run;



data ddd;
set dss;
if age = _n_  then age= 20 ;
proc print;
run;

I want replace all age values with 20 

[PaigeMiller · Accepted solution]

data dss;
    set sashelp.class;
    age=20;
run;

[AMSAS]

To understand what your code is doing, I recommend you look at the Automatic Variables documentation.

_N_ is initially set to 1. Each time the DATA step loops past the DATA statement, the variable _N_ increments by 1. The value of _N_ represents the number of times the DATA step has iterated.

As your IF statement is comparing _n_ with the variable age (sashelp.class) then you probably only set a single observation to 20. Observation #11 is Joyce and her age is 11, as _n_ would be 11 and age is 11 then you set age to 20 for that single observation.