Module 6: More Advanced Data Handling

Question 1

T/F: Automatic variables are temperaray

Answer 1

True

Question 2

How does SAS identify the beginning and end of the temporary variables?

Answer 2

When a dataset is sorted, SAS identifies it by the By group and creates first. and last. temporary variables.

Question 3

What are the four different combinations of first and last variables and what do they represent?

Answer 3

1) first = 1 last = 0, identifies first variable
2) first=0 last=1, identifies the last variable
3) first=0 last=0, identifies neither first or last (middle)
4) first=1 last=1, identifies first and last observation (only 1 variable)

Question 4

T/F: You do not need to create permanent variables to reference automatic variables outside of the first data step.

Answer 4

False: You do. Automatic variables can only be accessed in the dataset they are created unless assigned to a permanent variable.

Question 5

What happens to automatic variables when data is sorted by multiple variables?

Answer 5

Automatic variables are created for each sorted variable. The second variable automatics account for first and last values for each of the first sorted value.

Question 6

What are the automatic variables N and Error?

Answer 6

N: the number of times SAS has looped through the DATA step
Error: equal to 1 if there is a data error for an observation and otherwise zero

Question 7

T/F: N always equals the observation number

Answer 7

False: If there is a subsetting statemenet, a Merge statement, etc then the observation number and the number of iterations of the DATA step are not the same.

Question 8

What does the Retain statement do?

Answer 8

It keeps the value of the variable of interest unchanged in the PDV from one observation to the next.
Also creates a variable it if does not exist

Question 9

Fill in the blank:

The retain statement has no effect on varaibles read in with ___ and ___ statements.

Answer 9

Set and Merge