Search notes:
SAS: missing values
Variables that were not explicitly assigned a value have a missing value.
Three types of missing values:
The representation of a missing numeric value is controlled by the
missing option.
Missing character values are represented by a single space (' ').
Special missing values
.a through .z and ._ are special missing numeric values.
Sort order of special missing numeric values
%macro add_record(representation);
col_num = &representation ;
col_val ="&representation";
output;
%mend add_record;
data tq84_num_missing;
%add_record(42)
%add_record( .)
%add_record( 0)
%add_record(.q)
%add_record(.a)
%add_record(-3)
%add_record(._)
run;
/* Sorting the data set.
The lowest order has ._ followed by the
ordinary missing value (.) followed by
the special missing values .a through .z:
*/
proc sort
data=tq84_num_missing;
by col_num;
run;
proc print
data=tq84_num_missing;
run;
/*
Obs col_num col_val
1 _ ._
2 . .
3 A .a
4 Q .q
5 -3 -3
6 0 0
7 42 42
*/