Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of SAS/IML software. 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.
Here is a little trick to file away. Given a row vector of zeros and ones, thought of as representing a number in base 2, the following SAS/IML statements compute the decimal value of that vector. proc iml; x = {1 0 0 1 1 1}; /* number in base
One aspect of blogging that I enjoy is getting feedback from readers. Usually I get statistical or programming questions, but every so often I receive a comment from someone who stumbled across a blog post by way of an internet search. This morning I received the following delightful comment on
If you want to extract values from a SAS/IML vector, use the subscripting operation, such as in the following example: proc iml; x = {A B C D E}; y = x[{1 2 3}]; /* {A,B,C} */ The vector y contains the first three elements of x. However, did you
Sometimes you want to label only certain observations in a plot. This is useful in many ways, but one use is to label outliers on a scatter plot. In the SGPLOT procedure, the DATALABEL= option enables you to specify the name of a variable that is used to label observations.
I was at the Wikipedia site the other day, looking up properties of the Chi-square distribution. I noticed that the formula for the median of the chi-square distribution with d degrees of freedom is given as ≈ d(1-2/(9d))3. However, there is no mention of how well this formula approximates the
What do you call an interview on Twitter? A Tw-interview? A Twitter-view? Regardless of what you call it, I'm going to be involved in a "live chat" on Twitter this coming Thursday, 10NOV2011, 1:30–2:00pm ET. The hashtag is #saspress. Shelly Goodin (@SASPublishing) and SAS Press author recruiter Shelley Sessoms (@SSessoms)
Last week I showed how to use the UNIQUE-LOC technique to iterate over categories in a SAS/IML program. The observant reader might have noticed that the algorithm, although general, could be made more efficient if the data are sorted by categories. The UNIQUEBY Technique Suppose that you want to compute
Being able to reshape data is a useful skill in data analysis. Most of the time you can use the TRANSPOSE procedure or the SAS DATA step to reshape your data. But the SAS/IML language can be handy, too. I only use PROC TRANSPOSE a few times per year, so
I was recently asked the following question: I am using bootstrap simulations to compute critical values for a statistical test. Suppose I have test statistic for which I want a p-value. How do I compute this? The answer to this question doesn't require knowing anything about bootstrap methods. An equivalent
When you analyze data, you will occasionally have to deal with categorical variables. The typical situation is that you want to repeat an analysis or computation for each level (category) of a categorical variable. For example, you might want to analyze males separately from females. Unlike most other SAS procedures,
