Top 100 SAS Interview Questions and Answers for 2019

This article includes most frequently asked SAS interview questions which would help you to crack SAS Interview with confidence. It covers basic, intermediate and advanced concepts of SAS which outlines topics on reading data into SAS, data manipulation, reporting, SQL queries and SAS Macros. It includes questions ranging from simple theoretical concepts to tricky interview questions which are generally asked in freshers and experienced SAS programmers' interview.

1. Difference between INPUT and INFILE

The INFILE statement is used to identify an external file while the INPUT statment is used to describe your variables.
FILENAME TEST 'C:\DEEP\File1.xls';
DATA READIN;
INFILE TEST;
LENGTH NAME $25;
INPUT ID NAME$ SEX;
RUN;
Note : The variable name, followed by $ (dollar sign), idenfities the variable type as character. In the example shown above, ID and SEX are numeric variables and Name a character variable.

2. Difference between Informat and Format

Informats read the data while Formats write the data. Informat - To tell SAS that a number should be read in a particular format. For example: the informat mmddyy6. tells SAS to read the number121713as the date December 17, 2013. Format - To tell SAS how to print the variables.

3. Difference between Missover and Truncover

Missover -When the MISSOVER option is used on the INFILE statement, the INPUT statement does not jump to the next line when reading a short line. Instead, MISSOVER setsvariables to missing. Truncover - It assigns the raw data value to the variable even if the value is shorter than the length that is expected by the INPUT statement. The following is an example of an external file that contains data:
1
22
333
4444
This DATA step uses the numeric informat 4. to read a single field in each record of raw data and to assign values to the variable ID.
data readin;
infile 'external-file' missover;
input ID4.;
run;
proc print data=readin;
run;
The output is shown below :
Obs    ID
 1          .
 2          .
 3          .
 4      4444
Truncover
data readin;
infile 'external-file' truncover;
input ID4.;
run;
proc print data=readin;
run;
The output is shown below :
Obs    ID
 1      1
 2      22
 3      333
 4      4444

4. Purpose of double trailing@@ in Input Statement ?

The double trailing sign (@@)tells SAS rather than advancing to a new record, hold the current input record for the execution of the next INPUT statement.
DATA Readin;
   Input Name $ Score @@;   
   cards;
Sam 25 David 30 Ram 35
Deeps 20 Daniel 47 Pars 84
   ;
RUN;
The output is shown below :
Double Trailing

5. How to include or exclude specific variables in a data set?

- DROP, KEEP Statements and Data set Options
DROP, KEEP Statement

The DROP statement specifies the names of the variables that you want to remove from the data set.
data readin1;
set readin;
drop score;
run;
The KEEP statement specifies the names of the variables that you want to retain from the data set.
data readin1;
set readin;
keep var1;
run;
DROP, KEEP Data set Options

The main difference between DROP/ KEEP statement and DROP=/ KEEP=data set option is that you can not use DROP/KEEP statement in procedures.
data readin1 (drop=score);
set readin;
run;
data readin1 (keep=var1);
set readin;
run;

6. How to print observations 5 through 10 from a data set?

The FIRSTOBS= and OBS=data set options would tell SAS to print observations 5 through 10 from the data set READIN.
proc print data = readin (firstobs=5 obs=10);
run;

7.What are the default statistics that PROC MEANS produce?

PROC MEANS produce the “default” statistics of N, MIN, MAX, MEAN and STD DEV.

Proc Means : Detailed Explanation

8. Name and describe functions that you have used for data cleaning?

SAS Character Functions
Tutorial : Character Functions

9.Difference between FUNCTION and PROC

Example : MEAN function and PROC MEANS

The MEAN function is an average of the value of several variables in one observation.

The average that is calculated using PROC MEANS is the sum of all of the values of a variable divided by the number of observations in the variable.

In other words,The MEAN function will sum across the row and a procedure will SUM down a column.

MEAN Function
AVG=MEAN (of Q1 - Q3);
See the output below :
MEAN Function Output

PROC MEANS
PROC MEANS DATA=READIN MEAN;
RUN;
The output is shown below :
PROC MEANS Output

10. Differences between WHERE and IF statement?

For detailed explanation, see this tutorial -SAS : Where Vs IF
  1. WHERE statement can be used in procedures to subset data while IF statement cannot be used in procedures.
  2. WHERE can be used as a data set option while IF cannot be used as a data set option.
  3. WHERE statement is more efficient than IF statement. It tells SAS not to read all observations from the data set
  4. WHERE statement can be used to search for all similar character values that sound alike while IF statement cannot be used.
  5. WHERE statement can not be used when reading data using INPUT statement whereas IF statement can be used.
  6. Multiple IF statements can be used to execute multiple conditional statements
  7. When it is required to use newly created variables, useIF statement as it doesn't require variables to exist in the READIN data set

11.What is Program Data Vector (PDV)?

PDV is a logical area in the memory.

How PDV is created?
SAS creates a dataset one observation at a time.Input buffer is created at the time of compilation, for holding a record from external file.PDV is created followed by the creation of input buffer.SAS builds dataset in the PDV area of memory.

Detailed Explanation : How PDV Works

12. What is DATA _NULL_?

The DATA _NULL_ is mainly used to create macro variables. It can also be used to write output without creating a dataset.The idea of "null" here is that we have a data step that actually doesn't create a data set.

13. What is the difference between '+' operator and SUM function?

SUM function returns the sum of non-missing arguments whereas “+” operator returns a missing value if any of the arguments are missing.

Suppose we have a data set containing three variables - X, Y and Z. They all have missing values. We wish to compute sum of all the variables.
data mydata2;
set mydata;
a=sum(x,y,z);
p=x+y+z;
run;
The output is shown in the image below :
SAS : SUM Function vsPlus Operator
In the output, value of p is missing for 4th, 5th and 6th observations.

14. How to identify and remove unique and duplicate values?

1. Use PROC SORT with NODUPKEY and NODUP Options.
2. Use First. and Last. Variables - Detailed Explanation

The detailed explanation is shown below :

SAMPLE DATA SET
ID Name Score
1David45
1David74
2Sam45
2Ram54
3Bane87
3Mary92
3Bane87
4Dane23
5Jenny87
5Ken87
6Simran63
8Priya72

Create this data set in SAS
data readin;
input ID Name $ Score;
cards;
1 David 45
1 David 74
2 Sam 45
2 Ram 54
3 Bane 87
3 Mary 92
3 Bane 87
4 Dane 23
5 Jenny 87
5 Ken 87
6 Simran 63
8 Priya 72;
run;
There are several ways to identify and remove unique and duplicate values:

PROC SORT
In PROC SORT, there are two options by which we can remove duplicates.

1. NODUPKEY Option 2. NODUP Option

The NODUPKEY option removes duplicate observations where value of a variable listed in BY statement is repeated while NODUP option removes duplicate observations where values in all the variables are repeated (identical observations).
PROC SORT DATA=readin NODUPKEY;
BY ID;
RUN;
PROC SORT DATA=readin NODUP;
BY ID;
RUN;
The output is shown below :
SAS : NODUPKEY vs NODUP

The NODUPKEY has deleted 5 observations with duplicate values whereas NODUP has not deleted any observations.

Why no value has been deleted when NODUP option is used?
Although ID 3 has two identical records (See observation 5 and 7), NODUP option has not removed them. It is because they are not next to one another in the dataset and SAS only looks at one record back.

To fix this issue, sort on all the variables in the dataset READIN.
To sort by all the variables without having to list them all in the program, you can use the keywork ‘_ALL_’in the BY statement (see below).
PROC SORT DATA=readin NODUP;
BY _all_;
RUN;
The output is shown below :
SAS NODUP Output


PROC SORT - Detailed Explanation

15. Difference between NODUP and NODUPKEY Options?

The NODUPKEY option removes duplicate observations where value of a variable listed in BY statement is repeated while NODUP option removes duplicate observations where values in all the variables are repeated (identical observations).

See the detailed explanation for this question above (Q14).

16. What are _numeric_ and _character_ and what do they do?

1. _NUMERIC_ specifies all numeric variables that are already defined in the current DATA step.
2. _CHARACTER_ specifies all character variables that are currently defined in the current DATA step.
3. _ALL_ specifies all variables that are currently defined in the current DATA step.

Example : To include all the numeric variables in PROC MEANS
proc means;
var _numeric_;
run;
Tutorial : Specify a list of variables

17. How to sort in descending order?

Use DESCENDING keyword in PROC SORT code. The example below shows the use of the descending keyword.

PROC SORT DATA=auto; BY DESCENDING engine ; RUN ;

18. Under what circumstances would you code a SELECT construct instead of IF statements?

When you have a long series of mutually exclusive conditions and the comparison is numeric, using a SELECT group is slightly more efficient than using IF-THEN or IF-THEN-ELSE statements because CPU time is reduced.

The syntax for SELECT WHEN is as follows :
SELECT (condition);
WHEN (1) x=x;
WHEN (2) x=x*2;
OTHERWISE x=x-1;
END;

Example :
SELECT (str);
WHEN ('Sun') wage=wage*1.5;
WHEN ('Sat') wage=wage*1.3;
OTHERWISE DO;
wage=wage+1;
bonus=0;
END;
END;

19. How to convert a numeric variable to a character variable?

You must create a differently-named variable using the PUT function.

The example below shows the use of the PUT function.
charvar=put(numvar, 7.) ;

20. How to convert a character variable to a numeric variable?

You must create a differently-named variable using theINPUTfunction.

The example below shows the use of the INPUT function.
numvar=input(charvar,4.0);

21. What's the difference between VAR A1 - A3 and VAR A1 -- A3?

Single Dash :It is used to specify consecutively numbered variables. A1-A3 implies A1, A2 and A3.
Double-dash :It is used to specify variables based on the order of the variables as they appear in the file,regardless of the name of the variable. A1--A3 implies all the variables from A1 to A3 in the order they appear in the data set.
Example :The order of variables in a data set : ID Name A1 A2 C1 A3
So using A1-A3 would returnA1 A2 A3. A1--A3 would returnA1 A2 C1 A3.

22. Difference between PROC MEANS and PROC SUMMARY?

1. Proc MEANS by default produces printed output in the OUTPUT window whereas Proc SUMMARY does not. Inclusion of the PRINT option on the Proc SUMMARY statement will output results to the output window.
2. Omitting the var statement in PROC MEANS analyses all the numeric variable whereasOmitting the variable statement in PROC SUMMARY produces a simple count of observation.

How to produce output in the OUTPUT window using PROC SUMMARY?
Use PRINT option.
proc summary data=retail print;
 class services;
 var investment;
run;

23. Can PROC MEANS analyze ONLY the character variables?

No, Proc Means requires at least one numeric variable.

24. How SUBSTR function works?

The SUBSTR function is used to extract substring from a character variable.
The SUBSTR function has three arguments:
SUBSTR ( character variable, starting point to begin reading the variable, numberof characters to read from the starting point)
There are two basic applications of the SUBSTR function:
RIGHT SIDE APPLICATION
data _null_ ;                                                             
phone='(312) 555-1212' ;                                                      
area_cd=substr(phone, 2, 3) ;                                                    
put area_cd=;                                                            
run;
Result : In the log window, it writes area_cd=312 .
LEFT SIDE APPLICATION
It is used to change just a few characters of a variable. data _null_ ; phone='(312) 555-1212' ; substr(phone, 2, 3)='773' ; put phone=; run ; Result : The variable PHONE has been changed from(312) 555-1212 to (773) 555-1212.
Explanation : Other Character Functions

25. Difference between CEIL and FLOOR functions?

The ceil function returns the smallest integer greater than/equal to the argument whereas the floor returns the greatest integer less than/equal to the argument.
For example : ceil(4.4) returns 5 whereas floor(4.4) returns 4.

26. Difference between SET and MERGE?

SET concatenates the data sets where as MERGE matches the observations of the data sets.

SET SAS SET STATEMENT
MERGE Join Horizontally
Detailed Explanation : Data Step Merging
Detailed Explanation : Combine Data Sets

27. How to do Matched Merge and output only consisting of observations from both files?

Use IN=variable in MERGE statements. It is used for matched merge to track and select which observations in the data set from the merge statement will go to a new data set.

data readin;
merge file1(in=infile1) file2(in=infile2);
by id;
if infile1=infile2;
run;

28. How to do Matched Merge and output consisting of observations in file1 but not in file2, or in file2 but not in file1?

data readin;
merge file1(in=infile1)file2(in=infile2);
by id;
if infile1 ne infile2;
run;
SAS Merge

29. How to do Matched Merge and output consisting of observations from only file1?

data readin;
merge file1(in=infile1)file2(in=infile2);
by id;
if infile1;
run;

30. How do I create a data set with observations=100, mean 0 and standard deviation 1?

data readin;
do i=1 to 100;
     temp=0 + rannor(1) * 1;
     output;
end;
run;
proc means data=readin mean stddev;
var temp;
run;

31. How to label values and use it in PROC FREQ?

Use PROC FORMAT to set up a format.

proc format;
value score 0 - 100=‘100-‘
101 - 200=‘101+’
other=‘others’
;
proc freq data=readin;
tables outdata;
format outdatascore. ;
run;

Tutorial : PROC FREQ Detailed Explanation

32. How to use arrays to recode set of variables?

Recode the set of questions: Q1,Q2,Q3...Q20 in the same way: if the variable has a value of 6 recode it to SAS missing.
data readin;
set outdata;   
array Q(20) Q1-Q20;
do i=1 to 20;
if Q(i)=6 then Q(i)=.;
end;
run;

SAS Arrays and Do Loops Made Easy

33. How to use arrays to recode all the numeric variables?

Use _numeric_ and dim functions in array.
data readin;
set outdata;   
array Q(*) _numeric_;
do i=1 to dim(Q);
if Q(i)=6 then Q(i)=.;
end;
run;
Note : DIM returns a total count of the number of elements in array dimension Q.

34. How to calculate mean for a variable by group?

Suppose Q1 is a numeric variable and Age a grouping variable. You wish to compute mean for Q1 by Age.
PROC MEANS DATA=READIN;
VAR Q1;
CLASS AGE;
RUN;

35. How to generate cross tabulation?

Use PROC FREQ code.
PROC FREQ DATA=auto;
 TABLES A*B ;
RUN;
SAS will produce table of A by B.

36. How to generate detailed summary statistics?

Use PROC UNIVARIATE code.
PROC UNIVARIATE DATA=READIN;
 CLASS Age;
 VAR Q1;
RUN;
Note : Q1 is a numeric variable and Age a grouping variable.

37. How to count missing values for numeric variables?

Use PROC MEANS with NMISSoption.
Types of Missing Values in SAS

38. How to count missing values for all variables?

proc format;
value $missfmt ' '='Missing' other='Not Missing';
value missfmt .='Missing' other='Not Missing';
run;
proc freq data=one; 
format _CHAR_ $missfmt.;
tables _CHAR_ / missing missprint nocum nopercent;
format _NUMERIC_ missfmt.;
tables _NUMERIC_ / missing missprint nocum nopercent;
run;

39. Describe the ways in which you can create macro variables

There are 5 ways to create macro variables:
  1. %Let
  2. Iterative %DO statement
  3. Call Symput
  4. Proc SQl into clause
  5. Macro Parameters.
Detailed Tutorial : SAS Macros Made Easy

40. Use of CALL SYMPUT

CALL SYMPUT puts the value from a dataset into a macro variable.
proc means data=test;
var x;
output out=testmean mean=xbar;
run;
data _null_;
set testmean;
call symput("xbarmac",xbar);
run;

%put mean of x is &xbarmac;

41. What are SYMGET and SYMPUT?

SYMPUT puts the value from a dataset into a macro variable where as
SYMGET gets the value from the macro variable to the dataset.

Tutorial - Difference between SYMGET and SYMPUT

42. Which date function advances a date, time or datetime value by a given interval?

INTNX function advances a date, time, or datetime value by a given interval, and returns a date, time, or datetime value. Ex: INTNX(interval,start-from,number-of-increments,alignment).

Tutorial : INTNX Function with Examples

43. How to count the number of intervals between two given SAS dates?

INTCK(interval,start-of-period,end-of-period) is an interval function that counts the number of intervals between two give SAS dates, Time and/or datetime.

Tutorial : INTCK Function Explained

44. Difference between SCAN and SUBSTR?

SCAN extracts words within a value that is marked by delimiters. SUBSTR extracts a portion of the value by stating the specific location. It is best used when we know the exact position of the sub string to extract from a character value.

45. The following data step executes:

Data strings;
Text1=“MICKEY MOUSE & DONALD DUCK”;
Text=scan(text1,2,’&’);
Run;

What will the value of the variable Text be?

* DONALD DUCK [(Leading blanks are displayed using an asterisk *]

46. For what purpose would you use the RETAIN statement?

A RETAIN statement tells SAS not to set variables to missing when going from the current iteration of the DATA step to the next. Instead, SAS retains the values.

Tutorial : RETAIN Statement

47. When grouping is in effect, can the WHERE clause be used in PROC SQL to subset data?

No. In order to subset data when grouping is in effect, the HAVING clause must be used. The variable specified in having clause must contain summary statistics.
PROC SQL Made Easy

48. How to use IF THEN ELSE in PROC SQL?

PROC SQL;
SELECT WEIGHT,
CASE
WHEN WEIGHT BETWEEN 0 AND 50 THEN ’LOW’
WHEN WEIGHT BETWEEN 51 AND 70 THEN ’MEDIUM’
WHEN WEIGHT BETWEEN 71 AND 100 THEN ’HIGH’
ELSE ’VERY HIGH’
END AS NEWWEIGHT FROM HEALTH;
QUIT;

49. How to remove duplicates using PROC SQL?

Proc SQL noprint;
Create Table inter.Merged1 as
Select distinct * from inter.readin ;
Quit;

50. How to count unique values by a grouping variable?

You can use PROC SQL with COUNT(DISTINCT variable_name) to determine the number of unique values for a column.

51. How to merge two data sets using PROC SQL?

PROC SQL Merging

52. Difference between %EVAL and %SYSEVALF

%EVAL cannot perform arithmetic calculations with operands that have the floating point values. It is when the %SYSEVALF function comes into picture.
%let last=%eval (4.5+3.2);
%let last2=%sysevalf(4.5+3.2);
%put &last2;

53. How to debug SAS Macros

There are some system options that can be used to debug SAS Macros:
MPRINT, MLOGIC, SYMBOLGEN.
Detailed Tutorial : SAS Macros Made Easy

54.

%let x=temp;
%let n=3;
%let x3=result;
%let temp3=result2;

Difference between &x&n , &&x&n , &&&x&n ?

Solution : Multiple Ampersand Macro Variables

55. How to save log in an external file

Use PROC PRINTTO
proc printto log="C:\Users\Deepanshu\Downloads\LOG2.txt" new;
run;

56. How Data Step Merge and PROC SQL handle many-to-many relationship?

Data Step MERGE does not create a cartesian product incase of a many-to-many relationship. Whereas, Proc SQL produces a cartesian product.

SAS : Many-to-Many Merge

57. What is the use of 'BY statement' in Data Step Merge?

Without 'BY' statement, Data Step Merge performs merging without matching. In other words, the records are combined based on their relative position in the data set. The second data set gets placed to the "right" of the first data set (no matching based on the unique identifier - if data is not sorted based on unique identifier, wrong records can be merged).

When you use 'BY' statement, it matches observations according to the values of the BY variables that you specify.

58. Use of Multiple SET Statments

SAS : Use of Multiple SET Statements

59. How to combine tables vertically with PROC SQL


PROC SQL : Combine tables vertically

60. Two ways to reverse order of data

Reverse order of data

61. Which is more faster- Data Step / Proc SQL

The SQL procedure performed better with the smaller datasets (less than approx. 100 MB) whereas the data step performed better with the larger ones (more than approx. 100 MB).
It is because the DATA step handles each record sequentially so it never uses a lot of memory, however, it takes time to process one at a time. So with a smaller dataset, the DATA step is going to take more time sending each record through.
With the SQL procedure, everything is loaded up into memory at once. By doing this, the SQL procedure can process small datasets rather quickly since everything is available in memory. Conversely, when you move to larger datasets, your memory can get bogged down which then leads to the SQL procedure being a little bit slower compared to the DATA step which will never take up too much memory space.
If you need to connect directly to a database and pull tables from there, then use PROC SQL.
Related Posts
About Author:

Deepanshu founded ListenData with a simple objective - Make analytics easy to understand and follow. He has over 8 years of experience in data science. During his tenure, he has worked with global clients in various domains like Banking, Insurance, Telecom and Human Resource.

Next → ← Prev
Love this Post? Spread the Word!
Share