Construct a stacked bar chart in SAS where each bar equals 100%

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I enjoy reading the Graphically Speaking blog because it teaches me a lot about ODS statistical graphics, especially features of the SGPLOT procedure and the Graph Template Language (GTL). Yesterday Sanjay blogged about how to construct a stacked bar chart of percentages so that each bar represents 100%. His chart had the additional feature of displaying the percentages for each category. His post showed how to use the SGPLOT procedure to duplicates the functionality of the G100 option in the GCHART procedure.

In this blog post I present an alternative to Sanjay's construction. When I construct a stacked bar chart, I use PROC FREQ to compute the percentages of each category within a group. I then use the VBAR or HBAR statements in the SGPLOT procedure to construct the stacked bar chart. For example, the bar chart at the top of this post is constructed by using the following statements:

proc sort data=sashelp.cars(where=(Type^="Hybrid")) out=cars;
by Origin;                     /* sort X categories */
run;
 
proc freq data=cars noprint;
by Origin;                    /* X categories on BY statement */
tables Type / out=FreqOut;    /* Y (stacked groups) on TABLES statement */
run;
 
title "100% Stacked Bar Chart";
proc sgplot data=FreqOut;
vbar Origin / response=Percent group=Type groupdisplay=stack;
xaxis discreteorder=data;
yaxis grid values=(0 to 100 by 10) label="Percentage of Total with Group";
run;

The VBAR statement in the SGPLOT procedure creates the stacked bar chart. Each bar totals 100% because the Percent variable from PROC FREQ is used as the argument to the RESPONSE= option. The GROUPDISPLAY=STACK option stacks the groups so that there is one bar per category.

Creating stacked bars ordered by percentages

A variation of the 100% stacked bar chart is to order the "slices" of the bars by their relative sizes. This is shown at the left. I used the ORDER= option on the PROC FREQ statement to output the counts in descending order for each bar. If I use the GROUPORDER=DATA option on the VBAR statement in PROC SGPLOT, the categories will be arranged and colored according to how they appear in the data. In particular, the first bar will be ordered by relative percentages, as shown by the "Asia" bar. Notice, however, that this does not guarantee that other bars are ordered by size, as seen by the "Europe" bar.

Still, I like to order the groups by size because it makes it easier to find the relative percentages of the most important groups. In general, I prefer to order charts by some quantity, rather than to use the default alphabetical ordering.

The following statements produce the 100% stacked bar chart with ordered groups, assuming that the data set is already sorted according to the X variable:

proc freq data=cars order=freq noprint;  /* ORDER= sorts by counts within X */
by Origin;                               /* X var */
tables Type / out=FreqOutSorted;         /* Y var */
run;
 
proc print data=FreqOutSorted; run;
 
title "100% Stacked Bar Chart Ordered by Percentages";
proc sgplot data=FreqOutSorted;
vbar Origin / response=Percent group=Type 
              grouporder=data groupdisplay=stack; /* order by counts of 1st bar */
xaxis discreteorder=data;
yaxis grid values=(0 to 100 by 10) label="Percentage of Total with Group";
run;

PROC FREQ does it, too! (SAS 9.4m1)

Over the last few releases there have been quite a few new ODS graphs that come out of PROC FREQ "for free." If you have SAS 9.4m1, you can use the SCALE=GROUPPERCENT option to create a stacked bar chart similar to the one in the previous section:

proc freq data=cars order=freq;
tables Type*Origin / plots=freqplot(twoway=stacked scale=grouppct); 
run;

The lesson to learn is that you can use relatively simple statements (my post) to produce basic stacked bar charts or more sophisticated SAS code (Sanjay's post) to produce more complicated bar charts. Choose the method that you prefer, and let SAS do the rest.

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About Author

Rick Wicklin

Distinguished Researcher in Computational Statistics

Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of PROC IML and SAS/IML Studio. His areas of expertise include computational statistics, simulation, statistical graphics, and modern methods in statistical data analysis. Rick is author of the books Statistical Programming with SAS/IML Software and Simulating Data with SAS.

14 Comments

  1. Sanjay Matange
    Sanjay Matange on

    The SGPLOT VBAR statement can be used to created stacked grouped bars with FREQ statistics. With SAS 9.4, you can also use the PCTLEVEL option on the SGPLOT statement to get the G100 type bar with percent values. However, VBAR usage has some restrictions when it comes to overlaying other plot statements. So, to draw a G100 bar chart with % labels for each segment, we have to do it using a different statement like HIGHLOW bar. See my new blog article on the features of the HIGHLOW bar at http://blogs.sas.com/content/graphicallyspeaking/2014/05/04/the-highlow-plot/

    • Rick Wicklin

      Yes. Every ODS table and every ODS graph in SAS has a name. To exclude a table, put the statement
      ODS EXCLUDE name_of_table;
      before the PROC call. Use the ODS TRACE ON statement to find the name of tables. For this example, you would use
      ods exclude CrossTabFreqs;

  2. Sebastian Tilson on

    That worked perfectly! Thanks so much for always being so helpful; I've always enjoyed using the blog as a resource!

    Sebastian

  3. Hi Guys: I am trying to create a stacked horizontal bar graph which stacks over time with (1) Missing (2) Normal, and (3) Abnormal data then sums that using percentages. I can create this graph somewhat but I cant get it to use the % missing as % of the available data at each time point. Sas Missing basically uses missing as its own category and then all %'s are computed using the same N ie Missing+Available=N. Any ideas on how to get the graph I want? I would also like to add labels to the segments within the bar.
    This is the code I used from this website. thanks Guys.

    proc freq data=longabdata order=freq ;
    format step step.;
    format asbp100 abnm.;
    tables Asbp100*step / missing plots=freqplot(twoway=STACKED ORIENT=Horizontal scale=grouppcnt) ;
    run;

  4. Recently, I've been able to do this using the barchart statement in GTL. By using the GROUP100=MAGNITUDE option. This works fine when executing on my server (Linux). I've learned, however, that when executing local (Windows PC), I get an error\warning:

    WARNING 1-322: Assuming the symbol GROUP was misspelled as group100.

    The chart renders incorrectly. This is all in 9.4. Not sure why the local server space does this. Not a big deal, as I was only using it as a demo. It sure is a nice feature to have. It works very nice on the servers. Here's a full snippet of the code that works on the server:

    barchart category=date_label response=time_span_sec /
    group=module groupdisplay=stack orient=vertical
    name="sb2" group100=magnitude tipformat=(response=comma12.)
    TIP=(group response) TIPLABEL=(group="Module" response="Seconds")
    ;

    I'm charting the execution time (time_span_sec) of the code modules (module) of my daily executions (date_label). This creates a data vis for me to see how my program runs each day for easy debugging :). The 100% allows me to see how each module's execution time compares day by day.

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  6. I have used this code everything is perfect except for the y axis data point labels..they are taking too much space on the graph..I have values(35mg BD continuous N=6,50mg BD continuous N=13 and so..on and there are 10 doses that go on x-axis,so that will be 10 bars) but these bar labels are taking lots of space in the report..Is there an option where i can force label to flow into next line(35mg BD in first line and then continous in sec line and N+6 into third line)? please help me on this.

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