DSCI 325: Handout 9 Sorting and Options for Printing Data in SAS Spring 2017

Transcription

1 DSCI 325: Handout 9 Sorting and Options for Printing Data in SAS Spring 2017 There are a handful of statements (TITLE, FOOTNOTE, WHERE, BY, etc.) that can be used in a wide variety of procedures. For example, consider the following data set named MoviePrices.csv. Use the Import Data wizard to put this dataset into your personal SAS library. Consider the following PROC PRINT code that contains both TITLE and FOOTNOTE statements. PROC PRINT DATA=Hooks.MoviePrices; TITLE1 'Name of Data: Movie Prices'; TITLE2 'Data Source: Amazon'; FOOTNOTE1 'SalesRank is within Movies & TV Section'; Below is the resulting output from SAS. 1

2 Because the TITLE and FOOTNOTE statements are examples of global statements, they need not necessarily be placed within a PROC PRINT statement. Consider the following code which produces the same output as above. TITLE1 'Name of Data: Movie Prices'; TITLE2 'Data Source: Amazon'; FOOTNOTE1 'SalesRank is within Movies & TV Section'; PROC PRINT DATA=Hooks.MoviePrices; Also, note that the TITLE and FOOTNOTE statements will stay in effect until you replace them or cancel them. Thus, commenting out the titles and footnotes will have no effect. *TITLE1 'Name of Data: Movie Prices'; *TITLE2 'Data Source: Amazon'; *FOOTNOTE1 'SalesRank is within Movies & TV Section'; PROC PRINT DATA=Hooks.MoviePrices; To cancel a TITLE or FOOTNOTE statement, you can use the statements again with nothing specified. For example, the following code will cancel both titles and the footnote. TITLE1; TITLE2; FOOTNOTE1; PROC PRINT DATA=Hooks.MoviePrices; 2

3 USING THE WHERE STATEMENT As you have seen, the WHERE statement can be used to work with only a subset of a data set within a procedure (such as PROC PRINT). Using the WHERE statement within a procedure will tell SAS to perform the actions only on the data for which the WHERE condition is satisfied. Consider the following example in which the PROC PRINT prints information only when the Category is Comedy. PROC PRINT DATA=Hooks.MoviePrices; WHERE Category = 'Comedy'; The resulting SAS output: Tasks: 1. Use the WHERE command to print only movies whose SalesRank is less than Use the WHERE command to print only Comedy movies whose SalesRank is less than As mentioned previously, the WHERE statement can be used in a variety of procedures. Instead of using PROC PRINT, consider another procedure called PROC MEANS. This procedure calculates summary statistics (i.e., the mean, standard deviation, etc.). PROC MEANS data=hooks.movieprices; VAR SalesRank; Notice, the resulting output is a summary of SalesRank for all six movies. 3

4 The following code will obtain summary statistics for only the Comedy movies (note that N = 3 in the resulting output because only the three comedies were considered). PROC MEANS data=hooks.movieprices; VAR SalesRank; WHERE Category = 'Comedy'; The resulting SAS output: USING THE BY STATEMENT Similar to the WHERE statement, the BY statement can be used in various procedures. The effect of the BY statement is that any actions of a procedure are done piece-wise according to the variable specified in the BY statement. For example, consider the use of the BY statement in a PROC PRINT. PROC PRINT data=hooks.movieprices; BY Category; The resulting SAS output: 4

5 Next, consider a BY statement that includes a variable that has not been pre-sorted. PROC PRINT data=hooks.movieprices; BY SalesRank; Note that SAS prints only a few of the observations. A quick look at the log window explains why the above code did not produce the desired output PROC PRINT data=hooks.movieprices; 1132 BY SalesRank; 1133 ERROR: Data set HOOKS.MOVIEPRICES is not sorted in ascending sequence. The current BY group has SalesRank = 1952 and the next BY group has SalesRank = 373. NOTE: The SAS System stopped processing this step because of errors. NOTE: There were 3 observations read from the data set HOOKS.MOVIEPRICES. NOTE: PROCEDURE PRINT used (Total process time): real time 0.01 seconds cpu time 0.01 seconds Comment: In general, when you use a BY statement, you must first sort your observations by the variable(s) listed in your BY statement. The next section discusses how to sort data sets in SAS. 5

6 PROC SORT Sometimes it is necessary to sort your data. For example, as we just observed, the data must be pre-sorted in order for the BY statement to work properly. There may also be other times when it is convenient to sort your data by one or more variables, even if it isn t necessary to do so. In all of these situations, you can use PROC SORT. For example, the following program fixes the issue we had in the previous example. PROC SORT DATA=Hooks.MoviePrices OUT=MoviePrices2; BY SalesRank; Name of the data set you want to sort Tells SAS which variable(s) by which you want to sort the data Creates a new data set named MoviePrices2 that is sorted. You can omit this if you simply want to overwrite the original data set with the sorted values. Once the data has been pre-sorted by SalesRank, the following code will produce the desired outcome. PROC PRINT data=movieprices2; BY SalesRank; The resulting SAS output: Note that you could also sort in DESCENDING order using the DESCENDING option: PROC SORT DATA=Hooks.MoviePrices OUT=MoviePrices2; BY DESCENDING SalesRank; 6

7 PROC PRINT Consider the data in the file CourseEnrollments.txt. This data represents fictitious enrollments in classes over two semesters from four different faculty members. The following code can be used to read in this dataset. DATA CourseEnrollments; INFILE '/folders/myfolders/courseenrollments.txt'; INPUT Name $ Subject $4. CourseNum StartDate MMDDYY10. Section Credits Enrollment; PROC PRINT DATA=CourseEnrollments; 7

8 The following is the print-out produced by SAS. 8

9 As we have already discussed, SAS formats dates as the number of days that have passed since January 1, To override this default setting, a format statement can be specified in the PROC PRINT statement. PROC PRINT DATA=CourseEnrollments; FORMAT StartDate MMDDYY10.; Note that this formatting is also done in the labels provided at the top of the output that result from using the BY statement. Consider the following. PROC SORT DATA=CourseEnrollments; BY StartDate; PROC PRINT DATA=CourseEnrollments; BY StartDate; FORMAT StartDate MMDDYY10.; 9

10 There also exist some generic functions that can be used directly within a PROC PRINT statement to summarize a variable. For example, in the following program, the sum of enrollments is computed and printed with the raw date. PROC PRINT DATA=CourseEnrollments; BY StartDate; FORMAT StartDate MMDDYY10.; SUM Enrollment; Tells SAS to compute and display the column total for Enrollment. 10

11 USING PROC FORMAT We have already discussed the use of several different informats/formats available in SAS. You can find these formats and many more on the SAS support website: In addition to these formats automatically supported by SAS, you can also use PROC FORMAT to create your own format for variables. For instance, recall that in the previous example, StartDate = 09/10/2009 represented the Fall 2009 semester and StartDate = 01/15/2010 represented the Spring 2010 semester. Suppose that instead of using the actual dates when printing, we d like PROC PRINT to use Fall/Spring notation. The following code allows us to do this. PROC FORMAT; VALUE Semester = 'Fall 2009' = 'Spring 2010'; PROC PRINT DATA=CourseEnrollments; FORMAT StartDate Semester.; The VALUE statement allows you to create your own customized formats to display the data in a more meaningful way without altering the original variable name or variable type. Here, SAS will print Fall 2009 when the variable StartDate = The VALUE statement used above defines a format which you will refer to as Semester when you want to use it. In order for the format to take effect, you must associate the variable with the format you created using a FORMAT statement in the PROC PRINT step. A portion of the output is shown below. 11

12 The formatting statement works with the labels produced by the BY statement, as well. PROC PRINT DATA=CourseEnrollments; FORMAT StartDate Semester.; BY StartDate; A portion of the output is shown below. 12