SAS: Reading and Writing Data – Important Points and Interview Q&A

Important Points:

• Reading Data:
  • SAS offers various tools to read data from different sources:
    • SAS datasets (.sas7bdat): Use the SET statement to read existing SAS datasets.
    • CSV files: Use the INFILE statement with DELIMITER option to specify the delimiter (comma by default).
    • Excel files: Use procedures like PROC IMPORT or external libraries like SAS/ACCESS Interface to Excel.
    • Database tables: Use procedures like PROC SQL or SAS/ACCESS Interface to connect and read data from databases.
  • Important considerations:
    • Data formats (e.g., numeric, character, date) might need to be defined using informats during the reading process.
    • Missing values might require handling (e.g., replacing with a specific value).
• Writing Data:
  • SAS provides tools to create new SAS datasets or write data to external files:
    • SAS datasets: Use the DATA step to create a new SAS dataset and define variables.
    • CSV files: Use the FILE statement with PUT statements to write data in the desired format.
    • Excel files: Similar to reading, use procedures like PROC EXPORT or external libraries.
  • Important considerations:
    • Define variable formats when writing to external files to ensure proper representation.
    • Handle missing values consistently between reading and writing.

Sample Code (Reading CSV):

SAS

DATA mydata;
  INFILE 'C:\data\mydata.csv' DELIMITER=',';
  INPUT Var1 $20. Var2 num;  /* Define variable formats */
RUN;

Sample Code (Writing to CSV):

SAS

DATA _NULL_;
  FILE outfile FILENAME='C:\output\results.csv';
  PUT Var1 $20. Var2;
RUN;

Interview Questions and Answers:

1. What are the different ways to read data into SAS?

• You can read data from SAS datasets using the SET statement, from CSV files using the INFILE statement with a delimiter, from Excel files using PROC IMPORT or SAS/ACCESS, and from databases using PROC SQL or SAS/ACCESS Interface.

2. How do you handle missing values when reading data?

• You can define informats during the reading process to specify how missing values should be represented (e.g., a specific character code or numeric value). Alternatively, you can use functions like MISSING to identify missing values after reading the data.

3. What are some things to consider when writing data to a CSV file from SAS?

• You need to define the format of your variables (e.g., length for character variables, number of decimal places for numeric variables) using PUT statements to ensure the data is written correctly in the CSV file.
• You might also need to specify a delimiter (comma by default) to separate values in the output file.

4. Explain the difference between the SET and INFILE statements.

• SET is used to read existing SAS datasets, which are binary files specific to SAS.
• INFILE is used to read text-based data files like CSV, where you need to specify the delimiter and potentially data formats (informatics).

5. What are some advantages of using SAS datasets compared to CSV files?

• SAS datasets offer more efficient data storage and retrieval compared to text-based CSV files.
• SAS datasets can store additional information like variable labels and formats, which can be helpful for data management.

By understanding these points and practicing with sample code, you can effectively answer interview questions related to reading and writing data in SAS. Remember to adapt your answers to the specific context and functionalities mentioned in the question.