SAS

Question 1

what do we call statements that begin/end a step?

Answer 1

step boundaries e.g. run;

Question 2

what are global statements?

Answer 2

impact the entire SAS session and set options/values that will remain in effect until they are changed or the session ends e.g. title, options, libname, footnote

Question 3

how can you comment?

Answer 3

• in front of the line to comment one line
  /* comment */ for any length of text

Question 4

what are the 3 required attributes of a structured SAS column?

Answer 4

name (1-32ch, must start with letter/underscore), length (default numeric=8bytes/16digits, default char=length of column name, can be up to 32767bytes), type (char/numeric)

Question 5

how do you create/use a macrovariable?

Answer 5

use %LET statement to define macrovariable. WIthin code can then use & to refer to it.
e.g. %LET path = xyz
…&path
SAS will automatically replace path with xyz
macrovariables must have double quotations

Question 6

when defining a library, what is the method?

Answer 6

LIBNAME libname DATATYPE path libname must be <=8 characters.

Question 7

Which procedure produces a report about the descriptor portion of a table?

Answer 7

PROC CONTENTS

Question 8

what are rows and columns also called?

Answer 8

observations and variables

Question 9

Which statement can be used to subset the rows read in a PROC step?

Answer 9

WHERE

Question 10

Which procedure lists the distinct values for one or more columns?

Answer 10

PROC FREQ

Question 11

If you want to format just numeric or character types of columns, what keyword would you use?

Answer 11

format NUMERIC fmt;
format CHARACTER fmt;

for all columns use ALL

Question 12

describe the PROC MEANS step

Answer 12

generates simple summary statistics for each numeric column in input data by default unless VAR statement used

Question 13

in the PROC MEANS step, what does CLASS, WAYS, OUTPUT and OUT do?

Answer 13

CLASS - specifies columns to group by before calculating statistics
WAYS - specifies the number of ways to make unique combinations of class variables
OUTPUT - provides the option to create an output table with specific output statistics
OUT= - names output table to be created

Question 14

describe the PROC FREQ step

Answer 14

creates a frequency table for each variable in the input table by default. Can specify variables to be analysed using TABLES statement

Question 15

how do you import structured/unstructured data?

Answer 15

structured e.g. xlsx use LIBNAME or PROC IMPORT
unstructured e.g. CSV use PROC IMPORT

Question 16

in the PROC SORT step, what does NODUPKEY, DUPOUT do?

Answer 16

NODUPKEY keeps the first row for each unique value of the columns listed in the by statement
DUPOUT creates an output table containing duplicates

Question 17

In general, what are the 2 phases of the DATA step?

Answer 17

COMPILATION: creates PDV, establishes data attributed and rules for execution
EXECUTION: reads, manipulates and writes data

Question 18

what are the 2 default variables created in the DATA step?

Answer 18

N counts number of iterations through the data step when processing
ERROR initialised at 0 and goes up by 1 when any error detected in each iteration

Question 19

when to use DROP/KEEP vs DROP=/KEEP=?

Answer 19

DROP/KEEP added within the data step
DROP=/KEEP= added to a table on the DATA statement or SET statement
- when dropped/kept on SET statement, column is unavailable for processing in the DATA step

Question 20

DO UNTIL vs DO WHILE

Answer 20

DO UNTIL: condition checked at bottom of DO loop => always executes at least once
DO WHILE: condition checked at the top of DO loop => doesn’t iterate at all if condition is initially false

Question 21

describe the MERGE statement

Answer 21

all tables in the MERGE statement must be sorted by the column listed in the BY statement. it then combines tables where the BY columns match. Can use in= to subset using IF statement.

Question 22

what function do you use to convert
a) numeric to character
b) character to numeric

Answer 22

a) PUT(numeric-var, format)
b) INPUT(char-var, informat)

Question 23

how can you create a SAS date value?

Answer 23

MDY(month, day, year) function
TODAY() returns current date

Question 24

how can you increase a date by certain interval e.g. to last day of the following month

Answer 24

INTNX(interval, start-from, increment, alignment)
e.g. INTNX(‘month’, DATE-col, 1, ‘end’);

Question 25

how can you count the number of e.g. weeks between two dates?

Answer 25

INTCK(interval, start-from, end-date, method)
discrete counts weeks from Sundays, continuous counts 7 days as a week

Question 26

describe formats

Answer 26

formats are used to change the way values are displayed in data and reports - they do not actually change the underlying data values!

Question 27

what do WHERE statements work on ?

Answer 27

only work with columns existing in the input dataset, do not work with calculated columns

Question 28

What does SAS do when it encounters a syntax error?

Answer 28

first attempts to correct the error by attempting to interpret what you mean. Then SAS continues processing your program based on its assumptions. If SAS cannot correct the error, it prints an error message to the log.

Question 29

what colour is an error, note and warning message in the log?

Answer 29

red, blue, green

Question 30

what does the VALIDVARNAME=V7 option allow you to do?

Answer 30

-up to 32 characters.
-first character must begin with a letter or underscore. Subsequent characters can be letters of the Latin alphabet, numerals, or underscores.
- Trailing blanks are ignored.
- cannot contain blanks or special characters except for the underscore.
- can contain mixed-case letters. SAS stores and writes the variable name in the same case that is used in the first reference to the variable. However, when SAS processes a variable name, SAS internally converts it to uppercase. Therefore, you cannot use the same variable name with a different combination of uppercase and lowercase letters to represent different variables. For example, cat, Cat, and CAT all represent the same variable.
- Do not assign variables the names of special SAS automatic variables (such as N and ERROR) or variable list names (such as NUMERIC, CHARACTER, and ALL) to variables.

Question 31

what does the VALIDVARNAME=ANY option allow you to do?

Answer 31

• can begin with any character, including blanks
• leading blanks preserved, trailing blanks ignored

Question 32

whats the difference between formats and informats?

Answer 32

informats tell SAS how to read data, formats how to write/print data

Question 33

when do we add 1 to the number of times do loop has been executed?

Answer 33

when we don’t have an explicit output. With explicit output after each iteration we see e.g. 4 outputs. Without, SAS outputs after its gone through the last iteration which signalled it should stop e.g. 5 where it would have the same value as the one before (4). We only see the one row with iteration value of 5.

Question 34

what are the rules for creating a format name ?

Answer 34

• limited to 32 characters.
• Character format names must start with a dollar sign followed by a letter or underscore.
• Numeric format names must start with a letter or underscore.

Question 35

Define NOOBS

Answer 35

Suppress the column in the output that identifies each observation by number

Question 36

how can we write to the PUTLOG?

Answer 36

PUTLOG ALL; writes all columns/values in PDV to log
PUTLOG column=; writes selectee columns
PUTLOG “message”; writes a text string to log

Question 37

In DATA step processing, what are n and error?

Answer 37

The value of N represents the number of times the DATA step has iterated. N is initially set to 1. Each time the DATA step loops past the DATA statement, the variable N increments by 1.
ERROR is 0 by default but is set to 1 whenever an error is encountered, such as an input data error, a conversion error, or a math error, as in division by 0 or a floating point overflow.

Question 38

What are the steps of the Compilation phase?

Answer 38

1. Checks for syntax errors
2. Creates the program data vector (PDV)
3. Establishes the rules for processing data in the PDV e.g. flags which columns to be dropped/kept
4. Creates the descriptor portion of the output table

Question 39

What are the steps of the Execution phase?

Answer 39

1. Initialise the PDV
2. Read a row from the input table into the PDV
3. Sequentially processes statements and updates values in the PDV
4. At the end of the step, writes the contents of the PDV to the output table
5. Returns to top of DATA step

Question 40

when can you use IF vs WHEN subsetting?

Answer 40

Subsetting IF statements can only appear in DATA steps. In SAS, WHERE statements can be used in both DATA and PROC steps.

Question 41

when using MONTH() function, what does it return?

Answer 41

The MONTH function extracts the numeric month value from the specified date value. The MONTH function returns only the integer 1-12 without a leading zero.