Difference between IF and WHERE
http://basesasonlinetraining.blogspot.com/2015/07/Difference-between-if-and-where.html
One can subset dataset using IF or WHERE
statement to select specific observations from existing SAS data sets in order
to create a new SAS data set that includes only some of the observations from
the input data source.
Let us explore difference between IF and WHERE
at the ground level, below figure will explain processing of IF and WHERE at
PDV level.
As shown in the figure, WHERE conditions are
applied before the data enters the input buffer while IF conditions are applied
after the data enters the program data vector. This is the reason why the WHERE
condition is faster because not all observations have to be read and because it
can only be applied on variables that exist in the input data set.
Since WHERE is applied before PDV so it
makes automatic and new variables created in data step inaccessible to WHERE
statement, following table will summarize conditions where IF and WHERE
statements can be used –
