CONDITIONAL LOGIC IN THE DATA STEP

Transcription

1 CONDITIONAL LOGIC IN THE DATA STEP

2 Conditional Logic When processing data records, in many instances, the result to be obtained for the record depends on values of variable(s) within the record. Example: For the employees data, compute a raise and new salary for each employee. Raises are determined as: 2.5% for those in sales and marketing 3.2% for those in human resources 2.75% for all others To correctly compute the raise, the appropriate formula will have to be selected based on the value of the DIVISION variable.

3 IF-THEN-ELSE Structures One way to process conditionally is via an IF-THEN-ELSE set. Syntax: if <logical expression> then <expression>; So if the logical expression is true, the then expression is evaluated. An else statement can be added (note: it is a separate statement) if <logical expression> then <expression1>; else <expression2>; So if the logical expression is true, the first expression is evaluated, otherwise the second is. Of course the expression inside the else statement can be another if statement

4 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary;

5 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; Check this condition, if true

6 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; Check this condition, if true Assign raise with this.

7 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; If false Ignore this and

8 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; Check this condition, if true

9 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; Check this condition, if true Use this

10 IF-THEN-ELSE Structures A solution for computing the raises: data raises; Skip this if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; If false

11 IF-THEN-ELSE Structures A solution for computing the raises: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; And use this

12 Result

13 Result May want to check results for a few different conditions

14 SELECT Blocks The SELECT block is another tool that can perform operations conditionally. Syntax: select(expressiona); when (expression1) statement1; when (expression2) statement2; otherwise statement; end; SELECT is considered a code block, so an END statement is required. The OTHERWISE statement is required (though it can be empty) if the set of when expressions is not exhaustive.

15 SELECT Blocks A solution equivalent to the previous: data raises2; select(division); end; when('sales & MARKETING') raise=0.025*salary; when('human RESOURCES') raise=0.032*salary; otherwise raise=0.0275*salary;

16 SELECT Blocks A solution equivalent to the previous: data raises2; Compare this to each of these select(division); end; when('sales & MARKETING') raise=0.025*salary; when('human RESOURCES') raise=0.032*salary; otherwise raise=0.0275*salary; And use the expression corresponding to the match

17 SELECT Blocks A solution equivalent to the previous: data raises2; select(division); end; when('sales & MARKETING') raise=0.025*salary; when('human RESOURCES') raise=0.032*salary; otherwise raise=0.0275*salary; Unless there is none, then use the expression in the otherwise statement.

18 Finishing the Problem It remains to compute the new salary; however, this can be done unconditionally simply add the raise after it is computed. So, this: data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; new_salary = salary + raise;

19 Finishing the Problem Or, this: data raises2; select(division); when('sales & MARKETING') raise=0.025*salary; when('human RESOURCES') raise=0.032*salary; otherwise raise=0.0275*salary; end; new_salary = salary + raise;

20 Useful Tools In this case, the complete value of the division variable is not needed SCAN function: scan(expression, count <,list <,mod>>) expression is taken as evaluating to a character value count must evaluate to a whole number scan breaks up the string into words based on delimiters can be modified with list and mod the word at the count position is extracted from the expression

21 Useful Tools Example: data raises3; if scan(division,1) eq 'SALES' then raise=0.025*salary; else if scan(division,1) eq 'HUMAN' then raise=0.032*salary; else raise=0.0275*salary;

22 Useful Tools Example: data raises3; if scan(division,1) eq 'SALES' then raise=0.025*salary; Extract the first word from division else if scan(division,1) eq 'HUMAN' then raise=0.032*salary; else raise=0.0275*salary;

23 Useful Tools Example: data raises3; if scan(division,1) eq 'SALES' then raise=0.025*salary; Extract the first word from division else if scan(division,1) eq 'HUMAN' then raise=0.032*salary; else raise=0.0275*salary; Which makes for an easier comparison

24 Useful Tools Really, only the first letter is needed in this case SUBSTR function [substring]: substr(expression, start<,number>) expression is taken as evaluating to a character value start must evaluate to a whole number substr breaks up the string into individual characters removes the piece starting with the character at start, and reading the number of characters designated (if number omitted it reads to the end).

25 Useful Tools Example: data raises4; select(substr(division,1,1) ); when('s') raise=0.025*salary; when('h') raise=0.032*salary; otherwise raise=0.0275*salary; end;

26 Useful Tools Example: data raises4; select(substr(division,1,1) ); end; From division, start at the first character when('s') raise=0.025*salary; when('h') raise=0.032*salary; otherwise raise=0.0275*salary;

27 Useful Tools Example: data raises4; select(substr(division,1,1) ); end; From division, start at the first character when('s') raise=0.025*salary; when('h') raise=0.032*salary; otherwise raise=0.0275*salary; and read one character

28 Useful Tools Example: data raises4; select(substr(division,1,1) ); end; From division, start at the first character when('s') raise=0.025*salary; when('h') raise=0.032*salary; otherwise raise=0.0275*salary; and read one character So now comparison values are even more simple.

29 Useful Tools Since string matching is highly precise, both in terms of casing and spacing, some other useful functions are: lowcase(expression) upcase(expression) These do what you would expect Useful if casing is not consistent for values in the data. compress(expression <,chars> <,mod>) By default removes all blanks from the expression. Can use chars and mod to compress other characters out of an expression.

30 Exercise For the employees data, compute a raise and new salary for each employee. Raises are determined as: 2.5% for those who are pilots 3.2% for flight attendants 2.75% for mechanics 2.35% for all others Make a version using if-then-else and a version using select. Try to make your conditioning as simple as possible.

31 Exercise For the employees data, compute a raise and new salary for each employee. Raises are determined as: 3.2% for all level 3 employees 2.75% for all level % for all level % for any without a level Make a version using if-then-else and a version using select. Try to make your conditioning as simple as possible.

32 Working with Dates and Times Suppose we return to the original raise specification, but with one modification: Raises are determined as: 2.5% for those in sales and marketing 3.2% for those in human resources 2.75% for all others Plus a $2,500 flat increase for anyone with 30 or more years with the company (added after the percentage raise) I will need to condition on the date of hire also...

33 Working with Dates and Times We have seen that SAS dates are numbers (we ve used numeric formats for them, at least), what sort of numbers are they? SAS dates are stored as the number of days since January 1 st, 1960 (days before this have negative values). It would be impractical to directly figure out these values

34 Date Constants A date can be written in a basic form and be translated to a SAS date via a SAS date constant: 'DDMONYYYY'd In quotes, a date in date9 form is supplied with d appended to it to indicate it is a date, not a literal. SAS handles the conversion to days from 01JAN1960. To solve the problem, try:

35 Date Constants data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; if hiredate le ddmonyyyy d then bump=2500; else bump=0; new_salary=salary+raise+bump;

36 Date Constants data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; if hiredate le ddmonyyyy d then bump=2500; else bump=0; new_salary=salary+raise+bump; Need to fill in a specific date here that fits.

37 Date Constants data raises; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; if hiredate le ddmonyyyy d then bump=2500; else bump=0; new_salary=salary+raise+bump; Being careful here not to generate missing values.

38 Useful Functions Several functions are associated with dates (and times), a few useful ones include: today() Returns today s date as a SAS date (no arguments, but parentheses are required). yrdif(date1, date2, 'spec') Computes the difference between two dates (date2-date1) in years, based on a calendar spec. spec can be: 30/ day year/30 day months ACT Actual, including leap years ACT/360 or ACT/365 Divisor of 360 or 365

39 Useful Functions May have solved the previous with: data raisesb; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; if yrdif(hiredate,today(),'act') ge 30 then bump=2500; else bump=0; new_salary=salary+raise+bump;

40 Useful Functions May have solved the previous with: data raisesb; if division eq 'SALES & MARKETING' then raise=0.025*salary; else if division eq 'HUMAN RESOURCES' then raise=0.032*salary; else raise=0.0275*salary; if yrdif(hiredate,today(),'act') ge 30 then bump=2500; else bump=0; new_salary=salary+raise+bump; Compute the difference between today and the hire date, compare to 30 years.

41 Time Constants Times are measured in seconds from midnight. Likely an easier conversion, but time constants are also available: 'hh:mm't Quoted military time value, 00:00 to 23:59, with t appended. Can also add seconds: 'hh:mm:ss't Though constants are in military time, several formats are available.

42 Exercise Using the delay data set (an update to the flightdelays data set), create a departure category variable based on the following: Early morning: scheduled departure before 8 am Morning: scheduled departure between 8 am an noon Daytime: scheduled departure between noon and 6 pm Evening: after 6 pm

43 Exercise

44 Exercise Compute the actual departure time and supply it with a reasonable format:

45 Multiple Operations on a Condition Suppose we return to the previous raise specification, but with this modification: For anyone with 30 or more years with the company: 2.5% for those in sales and marketing 3.2% for those in human resources 2.75% for all other divisions For anyone with less: 1.5% for those in sales and marketing 1.75% for those in human resources 1.25% for all other divisions This instance requires multiple statements to be executed whether the hire date condition is true or false

46 Do Blocks The following is one solution: data raisesc; if yrdif(hiredate,today(),'act') ge 30 then do; select (scan(division,1)); when('sales') raise=0.025*salary; when('human') raise=0.032*salary; otherwise raise=0.0275*salary; end; end; else do; select (scan(division,1)); when('sales') raise=0.015*salary; when('human') raise=0.0175*salary; otherwise raise=0.0125*salary; end; end; new_salary=salary+raise;

47 Do Blocks The following is one solution: data raisesc; if yrdif(hiredate,today(),'act') ge 30 then do; select (scan(division,1)); when('sales') raise=0.025*salary; when('human') raise=0.032*salary; otherwise raise=0.0275*salary; end; end; else do; select (scan(division,1)); when('sales') raise=0.015*salary; when('human') raise=0.0175*salary; otherwise raise=0.0125*salary; end; end; new_salary=salary+raise; An arbitrary number of statements can be executed inside a do-end block.

48 Exercise For the employees data, compute a raise and new salary for each employee. Raises are determined as: 2.5% for level 1 or 2 pilots, 2.7% for level 3 3.2% for level 1 or 2 flight attendants, 3.5% for level % for level 1 or 2 mechanics, 3.0% for level % for all others