Advanced SAS Programming Techniques

Question 1

What is an index?

Answer 1

A file that stores values in ascending order for a variable or variables and includes information about the location of those values in the data file. It helps you access values directly rather than having SAS go down the rows until it finds a value.

Question 2

Syntax to create an INDEX in a DATA statement (for a simple and composite index)

Answer 2

This creates two simple indexes

For a simple index:

data datasetname (index=(column1 column2/unique));

set datasetname;

run;

For a composite index:

data datasetname (index=(indexname=(column1 column2)));

set datasetname

run;

Question 3

What option can you use to see information in the SAS log about index creation or index usage?

Answer 3

Default is n

options msglevel = i;

Question 4

When is an index not used? (3)

Answer 4

With a subsetting IF statement in a DATA step

With particular WHERE expressions

If SAS thinks it is more efficient to read the data sequentially

Question 5

Syntax to create or delete indexes on existing datasets with PROC DATASETS

Answer 5

NOLIST is optional. It suppresses the printing of the directory of SAS files in the SAS log and as ODS output.

proc datasets library = libref NOLIST;

modify datasetname;

index delete index-name;

index create index-specification;

quit;

Question 6

Syntax to create or delete indexes on an existing dataset with PROC SQL

Answer 6

proc sql;

create unique index index-name

on table-name(column1, column2);

drop index index-name from table-name;

quit;

Question 7

What information is printed out by the CONTENTS procedure or the CONTENTS statement in PROC DATASETS? (5)

Answer 7

• general and summary info
• engine/host dependent info
• alphabetic list of variables and attributes
• alphabetic list of integrity constraints
• alphabetic list of indexes and attributes

Question 8

Syntax for PROC CONTENTS

Syntax for PROC DATASETS with CONTENTS statement (2)

Answer 8

nolist is optional and suppresses the printing of the directory of SAS files in the SAS log and as ODS output.

proc contents data=libref.dataset;

run;

proc datasets library=libref nolist;

contents data=dataset;

quit;

proc datasets nolist;

contents data=libref.dataset;

quit;

Question 9

How do you list the contents of all files in a SAS library with PROC CONTENTS and with PROC DATASETS?

Answer 9

proc contents data=libref._all_;

run;

proc datasets library=libref nolist;

contents data=_all_;

quit;

Question 10

What happens to an index if you sort the data in place with the FORCE option in PROC SORT?

Answer 10

The index file is deleted

Question 11

How do you copy a data set to a new location using PROC DATASETS?

Using PROC COPY?

What happens if the data set contains an index?

Answer 11

A new index file is automatically created for the new data file

proc datasets library = old-libref nolist;

copy out = new-libref;

select datasetname;

quit;

proc copy out = new-libref in = old-libref

[move];

select datasetname;

run;

quit;

Question 12

How do you rename an indexed dataset so as to preserve the index?

Answer 12

Note the index is automatically renamed as well

proc datasets library=libref nolist;

change old-datasetname = new-datasetname;

quit;

Question 13

How do you rename variables within an indexed data set so as to preserve the index?

Answer 13

If you rename a variable for which there is a simple index, the index is also renamed. If the variable is used in a composite index, the composite index automatically references the new variable name.

proc datasets library=libref nolist;

modify datasetname;

rename oldvarname1 = newvarname1

oldvarname2 = newvarname2;

quit;

Question 14

How to combine raw data files vertically using FILENAME?

Answer 14

filename fileref (‘file-path1’ ‘file-path2’);

Question 15

COMPRESS function

Answer 15

default characters-to-remove is blank spaces

Allows you to remove characters from a string

compress(source-string, characters-to-remove);

Question 16

today function

Answer 16

Returns the current date from the system clock as a SAS date value

Question 17

INTCK function

Answer 17

INTCK(interval, start-date, end-date)

Returns the number of interval boundaries of a given kind that lie between two dates, times, or datetime values.

e.g.
monthnum = intck(‘month’, ‘25aug2000’d, ’05sep2000’d)

monthnum = 1

Question 18

INTNX function

Answer 18

INTNX(interval, start-from, increment)

Gives the date that corresponds to the beginning of the next interval

e.g.
next = intnx(‘month’, ‘25aug2000’d, 1)

next = 01sep2000

Question 19

Syntax for combining SAS data sets vertically using PROC APPEND

Answer 19

base names the data set to which you want to add obs

proc append base=sas-data-set data= sas-data-set;

run;

Question 20

What is more efficient to combine two SAS data sets vertically: PROC APPEND or a DATA step? Why?

Answer 20

PROC APPEND

Because it only reads the data in the DATA= data set, not the BASE= data set.

The DATA step SET statement would read both data sets

Question 21

What option can you use when you’re combining SAS data sets vertically using PROC APPEND and the DATA= dataset has more variables than the BASE= dataset?

Answer 21

Note that this will drop the extra variable

FORCE

proc append base=SAS-dataset data=SAS-dataset force;

run;

Question 22

Can you append (combine vertically) datasets when a common variable has different lengths in each dataset?

What option can you use to do it?

Answer 22

Note that truncating may occur

No, you will get an error

Use the FORCE option

Question 23

What happens when you’re appending datasets where a common variable has different data types?

How can you append the datasets?

What happens when you do this?

Answer 23

You’ll get an error.

Use the FORCE option

For the variable with the different data types, you’ll get missing values in the DATA= dataset.

Question 24

What happens when you’re appending datasets with PROC APPEND where the BASE= dataset has more variables than the DATA= dataset?

Answer 24

You get missing values for the extra variable

Question 25

ARRAY statement

Answer 25

ARRAY arrayname(#ofitems) [$] array-variables (actual-values)

e.g. ARRAY TIME(6) TIME1-TIME6 (36, 40, 10, 39, 97, 25)

Note: can use * to let SAS figure out the number of items

Question 26

How do you convert from character to numeric? From numeric to character?

Answer 26

Character to numeric:

INPUT(“text”, informat)

Numeric to character:

PUT(number, format)

Question 27

What is the max number of tables that can be joined at a time with PROC SQL?

Answer 27

256

Question 28

bufno= option

Answer 28

A larger number of buffers can speed up execution time by limiting the number of input and output (I/O) operations that are required for a particular SAS data set. However, the improvement in execution time comes at the expense of increased memory consumption.

Question 29

reuse = option

Answer 29

Tracks and recycles free space

By default, new observations are appended to existing compressed data sets. To track and reuse available space by deleting or updating other observations, use the REUSE= data set option when you create a compressed SAS data set.

Question 30

Characteristics of hash object key component (4)

Characteristics of hash object data component (2)

Answer 30

Key component:

• might consist of numeric and character values
• maps key values to data rows
• must be unique
• can be a composite

Data component:

• can contain multiple data values per key value
• can consist of numeric and character values

Question 31

FULLSTIMER Option

Answer 31

Specifies that SAS write to the SAS log a complete list of computer resources that were used for each step and for the entire SAS session.

Can aid in benchmarking

Question 32

SASFILE statement

Answer 32

Opens a SAS data set and allocates enough buffers to hold the entire file in memory.

Question 33

FILE statement

Answer 33

Specifies the current output file for PUT statements.