4 tricky SAS questions commonly asked in interview

Tavish Srivastava 25 Jun, 2019 • 5 min read

Introduction

While working extensively on SAS-EG, I lost touch of coding in Base SAS. I had to brush up my base SAS before appearing for my first lateral interview. SAS is highly capable of data triangulation, and what distinguishes SAS from other such languages is its simplicity to code.

There are some very tricky SAS questions and handling them might become overwhelming for some candidates. I strongly feel a need of a common thread which has all the tricky SAS questions asked in interviews. This article will give a kick start to such a thread. This article will cover 4 of such questions with relevant examples. This article is the first part of tricky SAS questions series. Please note that the content of these articles is based on the information I gathered from various SAS sources.

And if you’re looking to land your first data science role – look no further than the ‘Ace Data Science Interviews‘ course. It is a comprehensive course spanning tons of videos and resources (including a mammoth interview questions and answers guide).

 

[stextbox id=”section”]1. Merging data in SAS :[/stextbox]

Merging datasets is the most important step for an analyst. Merging data can be done through both DATA step and PROC SQL. Usually people ignore the difference in the method used by SAS in the two different steps. This is because generally there is no difference in the output created by the two routines. Lets look at the following example :

Merge

Problem Statement : In this example, we have 2 datasets. First table gives the product holding for a particular household. Second table gives the gender of each customer in these households. What you need to find out is that if the product is Male biased or neutral. The Male biased product is a product bought by males more than females. You can assume that the product bought by a household belongs to each customer of that household.

Thought process: The first step of this problem is to merge the two tables. We need a Cartesian product of the two tables in this case. After getting the merged dataset, all you need to do is summarize the merged dataset and find the bias.

 

Code 1

[stextbox id=”grey”]
Proc sort data = PROD out =A1; by household;run;
Proc sort data = GENDER out =A2; by household;run;
Data MERGED;
    merge A1(in=a) A2(in=b);
    by household;
    if a AND b;
run;[/stextbox]

Code 2 :

[stextbox id=”grey”]
PROC SQL;
     Create table work.merged as
           select t1.household,  t1.type,t2.gender
           from prod as t1, gender as t2
           where t1.household = t2.household;
quit; [/stextbox]

Will both the codes give the same result?

The answer is NO. As you might have noticed, the two tables have many-to-many mapping. For getting a cartesian product, we can only use PROC SQL. Apart from many-to-many tables, all the results of merging using the two steps will be exactly same.

Why do we use DATA – MERGE step at all?

DATA-MERGE step is much faster compared to PROC SQL. For big data sets except one having many-to-many mapping, always use DATA- MERGE.

[stextbox id=”section”]2. Transpose data-sets :[/stextbox]

When working on transactions data, we frequently transpose datasets to analyze data. There are two kinds of transposition. First, transposing from wide structure to narrow structure. Consider the following example :

transpose 1

Following are the two methods to do this kind of transposition :

a. DATA STEP :

[stextbox id=”grey”]
data transposed;set base;
        array Qtr{3} Q:;
        do i = 1 to 3;Period = cat('Qtr',i);Amount = Qtr{i} ;output;end;
        drop Q1:Q3;
        if Amount ne .;
run; [/stextbox]

b. PROC TRANSPOSE :

[stextbox id=”grey”]
proc transpose data = base out = transposed 
                (rename=(Col1=Amount) where=(Amount ne .)) name=Period;
by cust; run; [/stextbox]

In this kind of transposition, both the methods are equally good. PROC TRANSPOSE however takes lesser time because it uses indexing to transpose.

Second, narrow to wide structure. Consider an opposite of the last example.

transpose 2

For this kind of transposition, data step becomes very long and time consuming. Following is a much shorter way to do the same task,

[stextbox id=”grey”]
Proc transpose data=transposed out=base (drop=_name_) prefix Q;
       by cust;
       id period;
       var amount;
run; [/stextbox]

[stextbox id=”section”]3. Passing values from one routine to other:[/stextbox]

Imagine a scenario, we want to compare the total marks scored by two classes. Finally the output should be simply the name of the class with the higher score. The score of the two datasets is stored in two separate tables.

There are two methods of doing this question. First, append the two tables and sum the total marks for each or the classes. But imagine if the number of students were too large, we will just multiply the operation time by appending the two tables. Hence, we need a method to pass the value from one table to another. Try the following code:

Pass

[stextbox id=”grey”]
DATA _null_;set class_1;
       total + marks;
       call symputx ('class1_tot',total);
run;
DATA _null_;set class_2;
       total + marks;
       call symputx ('class2_tot',total);
run;
DATA results;
       if &class1_tot > &class2_tot then better_class = 1;
       else if &class1_tot > &class2_tot then better_class = 2;
       else better_class = 0;
run; [/stextbox]

Funtion symputx creates a macro variable which can be passed between various routines and thus gives us an opportunity to link data-sets.

[stextbox id=”section”]4. Using where and if : [/stextbox]

“Where” and “if” are both used for sub-setting. Most of the times where and if can be used interchangeably in data step for sub-setting. But, when sub-setting is done on a newly created variable, only if statement can be used. For instance, consider the following two programs,

[stextbox id=”grey”]

Code 1 :                                                                                  Code 2 :

data a;set b;                            data a;set b;
      z= x+y;                                  z= x+y;
      if z < 10;                               where z < 10;
run;                                     run; [/stextbox]

Code 2 will give an error in this case, because where cannot be used for sub-setting data based on a newly created variable.

[stextbox id=”section”]End Notes : [/stextbox]

These codes come directly from my cheat chit. What is especial about these 4 codes, that in aggregate they give me a quick glance to almost all the statement and options used in SAS. If you were able to solve all the questions covered in this article, we think you are up for the next level. You can read the second part of this article here ( https://www.analyticsvidhya.com/blog/2014/04/tricky-base-sas-interview-questions-part-ii/ ) . The second part of the article will have tougher and lengthier questions as compared to those covered in this article.

Have you faced any other SAS problem in analytics interview? Are you facing any specific problem with SAS codes?  Do you think this provides a solution to any problem you face? Do you think there are other methods to solve the problems discussed in a more optimized way? Do let us know your thoughts in the comments below.

You can read part II of this article here.

 

If you like what you just read & want to continue your analytics learning, subscribe to our emails or like our facebook page.

Tavish Srivastava 25 Jun 2019

Tavish Srivastava, co-founder and Chief Strategy Officer of Analytics Vidhya, is an IIT Madras graduate and a passionate data-science professional with 8+ years of diverse experience in markets including the US, India and Singapore, domains including Digital Acquisitions, Customer Servicing and Customer Management, and industry including Retail Banking, Credit Cards and Insurance. He is fascinated by the idea of artificial intelligence inspired by human intelligence and enjoys every discussion, theory or even movie related to this idea.

Frequently Asked Questions

Lorem ipsum dolor sit amet, consectetur adipiscing elit,

Responses From Readers

Clear

Priya Varshney
Priya Varshney 27 Nov, 2013

1. Merging data in SAS : is complete answer is Data A; Input household $ type_of_product $13.; Datalines; A savings A pension A investment B term B pension B investment C term C pension ; run; proc print; run; Data B; input household $ Customer $ gender $; datalines; A Ken M A Seni F B Fab M C Ron M C Mary F ; run; Proc sort data = a out =A1; by household;run; Proc sort data = b out =A2; by household;run; Data MERGED; merge A1(in=a) A2(in=b); by household; if a AND b; run; proc print data=merged; run; PROC SQL; Create table work.merged as select t1.household, t1.type,t2.gender from a as t1, b as t2 where t1.household = t2.household; quit; proc sort data=merged out=f; by type_of_product; run; data final; retain f 0; retain m 0; set f; by type_of_product; if gender="F" then f=f+1; if gender="M" then m=m+1; if last.type_of_product then do; if f>m then product_type="Female based"; else if m>f then product_type="Male based"; else product_type="Neutral"; output; f=0; m=0; end; drop household customer gender f m ; run; proc print data=final; run;

Anders Sköllermo
Anders Sköllermo 01 Jan, 2014

Hi! COMMENT to the answer to "4. Using where and if : " Suppose SAS-table B (WORK.B) contains a variable B, then the solution in Code 2 will work: data a;set b; z= x+y; /* The old value of Z, which was < 10, will be replaces. */ where z < 10; run; The WHERE-clause should (in my opinion) immediately follow the SET-statement. Easy question! Easy answer! Basic questions: What data do You have ? What rules do you have? What results do you want ? THEN we can start to discuss what is CORRECT and what is (perhaps) "a little less correct" (British English understatement). / Br Anders

sandy
sandy 24 Jan, 2014

Reply to answer 4 . Simple diff b/w IF and WHERE CLAUSE. IF works on pdv, where as WHERE works on source and applies conditions so new cant be created in WHERE. so there In code2 shows error.

Anders Sköllermo
Anders Sköllermo 25 Jan, 2014

Hi! Type error. My note should read: "Suppose SAS-table B (WORK.B) contains a variable Z, ..." (The drawback of writing the answers late at night..). In other words: If you have a variable Z and also create a variable Z, then the result depends strongly on the use of WERE (the old Z value) or IF (the newly calculated Z value). The programmers show give some thoughts to data structures, what variables are created where, what results are wanted. / Br Anders

Anders Sköllermo
Anders Sköllermo 25 Jan, 2014

Case 4: Bottom Line: Case 2 with WHERE may work "fine", without any errors at all.

bhanu
bhanu 28 Jan, 2014

Hi Tavish, I do know about base sas and macros but i want to know more about banking projects how it goes on the daily basis.I want to know about the work of the analyst in a banking domain from the scratch.Can u please help me in guiding me as u r also from the same domain.I really appreciate your efforts u r investing for the young professionals. Thanks in Anticipation Bhanu

Shivi
Shivi 10 Feb, 2014

Following on email

Anders Sköllermo
Anders Sköllermo 10 Feb, 2014

Hi! The real meaning of the WHERE-statement: The WHERE statement is (approximately) a WHERE data set option: data a; set b (where=(z < 10)); Z= x+y; run; The WHERE statement cannot be executed conditionally. That is, you cannot use it as part of an IF-THEN statement. (according to SAS9.3 manuals). data a; set b; where=z < 10; Z= x+y; run; Please note that the following is OK (but I would NEVER write like that) data a; where=z < 10; /* WHERE on SET WORK.B - not on WORK.A ! */ set b; Z= x+y; run; The following is OK and works as it should - BUT DO NOT USE IT !! data work.a; if x=1 then do; where=z < 10; end; /* The WHERE-part is a declaration and will always be used! */ set work.b; z= x+y; run; My way of writing SAS programs: Learn the actual syntax and functionality of all the parts that you use. Write very clear SAS-programs with a lot of documentation.

Anders Sköllermo
Anders Sköllermo 10 Feb, 2014

Use WHERE-data set option and IF statement together! It can be handy to use the WHERE data set option (perhaps written as the WHERE statement) to restrict what observation are used in the data step AND one or several IF statements do do further calculations and selections on these observations, using the newly calculated variables.

DaveG
DaveG 02 Mar, 2014

hi, good set of four questions. the proc transpose vs the data step: These programs do the same thing but they are *not* equivalent or equally useful. Why? The data step as programmed has to have 3 occurences per set, exactly three. The Proc transpose works for any number of occurences (and creates any number of variables when ging from thin to wide). In practical use this is important and I would not accept the assertion these methods are the same if I heard that in an interview.

DaveG
DaveG 02 Mar, 2014

BTW it is easy to do example 3 with one datastep and no macro variables. :)

priya
priya 12 May, 2014

alternative solution for case1 using proc sql: data one; infile datalines; input household $ product_type $10.; datalines; A Savings A Pension A Investment B Term B Pension B Investment C Term C Pension ; data two; infile datalines; input household $ Customer $ Gender $; datalines; A Ken M A Seni F B Fab M B Ron M C Mary F ; proc sort data=one; by household; run; proc sort data=two; by household; run; PROC SQL; Create table work.merged as select t1.household, t1.product_type,t2.gender from one as t1, two as t2 where t1.household = t2.household; create table male(drop=gender) as select distinct product_type as saving,gender,count(gender) as Male from merged group by saving,gender having gender='M'; create table female(drop=gender) as select distinct product_type as saving,gender,count(gender) as female from merged group by saving,gender having gender='F'; create table joined as select m.saving,male,female, case when male>female then 'Male-based' when female>male then 'Female-based' else 'Neutral' end as biased from male m,female f where m.saving=f.saving order by saving; quit;

Aparna Konda
Aparna Konda 27 May, 2014

What is the major difference between Datalines and Cards in SAS programming?

Anders
Anders 07 Jun, 2014

Comment about CARDS; and DATALINES; In 1976 when SAS was (officially) released, data were read from records 80 bytes broad. Often the data were included, so you first had the Data step, which ended with CARDS; statement. After that came the data rows. The end of the data cards / data rows was signalled using RUN; DATALINES means exactly the same as CARDS (as far as I know). Often it is better to store the data in a separate file, which you refer to using the INFILE statement. Then specify how to read the data using the INPUT statement. CARDS or DATLINES is not used. / BAr Anders

Amanpreet
Amanpreet 07 Nov, 2014

Hi Kunal, Nice questions above. Similarly can u share an example for nodup and nodupkey. This is confusing me. Thanks aman

Deep
Deep 31 Mar, 2015

Can we use proc sql to draw the final table instead of retain....( specially the count of gender male / female)

Arun
Arun 04 Jun, 2015

Hi I'm Arun from Bangalore, I work in reputed company as a SLM co-ordinator. I want to switch to a technology field and when i was looking found Analysts and SAS to be pretty interesting. I have around 9 years of industry experience in Service management. And my salary is around 10 lakhs per anum . Wanted to know if i switch my carrier now and do the relevant courses necessary for analysts and SAS will this be a wise idea. And in terms of finance as well will it be a wise move. Your comments are appreciated, Thanks

rsakumar
rsakumar 18 Jul, 2015

hai sir very good perform sas better understanding

pratik singh
pratik singh 02 Aug, 2015

As far as I have studied ...Comparing proc sql and datastep merge: When dataset is small both take appox same resource(for one to one and many to one)..but as the size increases proc sql starts getting better.Whether it be in terms of I/O operations time or space.(If the dataset is not already sorted) .I read in one of the SAS User Group Paper

Anders Sköllermo
Anders Sköllermo 29 Dec, 2015

3. Passing values from one routine to other: The following code: DATA _null_;set class_1; total + marks; call symputx ('class1_tot',total); run; Please note that this means that CALL SYMPUTX is called once in EVERY loop of the Data step. SO this works fine on small sets of data, but is Expensive on large sets of data. Suggested solution: DATA Sum_class_1; set class_1 end= endclass1; total + marks; if endclass1 then call symputx ('class1_tot',total); run; I have not made any test run, but the solution is basically OK). /Best Regards Anders DATA _null_;set class_2;

Shweta Gupta
Shweta Gupta 30 Nov, 2017

please give the answer: 1. Consider you have Sales Data and a variable Order_date is the Date of Order Placed. Write a Macro that will Display the Report of all the Sales Conducted on Daily Basis ? Example: If today is 01 January 2000, If I call macro today, It shows orders placed on 01 January 2000. If I call same macro on 02 January, It should give Report of orders placed on 02 January. - 2. Consider Same Sales Data, Write a Macro to get summarized report on any particular year ? Example: I want to run proc means on sales data for the year 2004, may be tomorrow I want to get for 2005 or so. - 3. Consider the Same Sales Data. Suppose you have 3 Types of Orders and a variable Order_type having values either Type 1 Type 2 or Type 3 for Each Order Placed and you have another variable Quantity, having the total number of quantities ordered for each order. Write a Macro to display the frequency of quantity ordered for given order type in any particular year. Example: If I mention value of year 2004 and type 3, It should display frequency of quantities placed in 2004 with type 3 with appropriate title. If I just mention year 2004, It should display frequency of all quantities ordered in 2004 with all types. - 4. Write a Macro to get pdf report of orders placed in range of years with appropriate title? Example: If I select range of years 2003 to 2006, I should get pdf report of orders placed in all these years separately on desktop. - 5. Write a Macro to get a Report for each year and each order type, so we get the mean of total_retail_price in the title ? Example: Suppose I choose year = 2001 and order_type = 2, It should display orders placed in these parameters and I also want the mean of total_retail_price in the title of the report. Thanks, Shweta

Data Visualization
Become a full stack data scientist
  • [tta_listen_btn class="listen"]