### About this blog

Rick Wicklin, PhD, is a distinguished researcher in computational statistics at SAS and is a principal developer of PROC IML and SAS/IML Studio. This blog focuses on statistical programming. It discusses statistical and computational algorithms, statistical graphics, simulation, efficiency, and data analysis. Rick is author of the books

*Statistical Programming with SAS/IML Software*and*Simulating Data with SAS*.

Follow @RickWicklin on Twitter.

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## Finding observations that satisfy multiple conditions: The LOC-ELEMENT technique

A common task in data analysis is to locate observations that satisfy multiple criteria. For example, you might want to locate all zip codes in certain counties within specified states. The SAS DATA step contains the powerful WHERE statement, which enables you to extract a subset of data that satisfy […]

Post a Comment ## Sum a series in SAS

A customer asked: How do we go about summing a finite series in SAS? For example, I want to compute for various integers n ≥ 3. I want to output two columns, one for the natural numbers and one for the summation of the series. Summations arise often in statistical […]

Post a Comment ## Vectors that have a fractional number of elements

The title of this article makes no sense. How can the number of elements (in fact, the number of anything!) not be a whole number? In fact, it can't. However, the title refers to the fact that you might compute a quantity that ought to be an integer, but is […]

Post a Comment ## Matrix multiplication with missing values in SAS

Sometimes I get contacted by SAS/IML programmers who discover that the SAS/IML language does not provide built-in support for multiplication of matrices that have missing values. (SAS/IML does support elementwise operations with missing values.) I usually respond by asking what they are trying to accomplish, because mathematically matrix multiplication with […]

Post a Comment ## Complete cases: How to perform listwise deletion in SAS

SAS procedures usually handle missing values automatically. Univariate procedures such as PROC MEANS automatically delete missing values when computing basic descriptive statistics. Many multivariate procedures such as PROC REG delete an entire observation if any variable in the analysis has a missing value. This is called listwise deletion or using […]

Post a Comment ## Creating an array of matrices

The SAS DATA step supports multidimensional arrays. However, matrices in SAS/IML are like mathematical matrices: they are always two dimensional. In simulation studies you might need to generate and store thousands of matrices for a later statistical analysis of their properties. How can you accomplish that unless you can create […]

Post a Comment ## Specify the order of variables at run time in SAS

In SAS, the order of variables in a data set is usually unimportant. However, occasionally SAS programmers need to reorder the variables in order to make a special graph or to simplify a computation. Reordering variables in the DATA step is slightly tricky. There are Knowledge Base articles about how […]

Post a Comment ## Detect empty parameters that are passed to a SAS/IML module

A SAS/IML programmer asked a question on a discussion forum, which I paraphrase below: I've written a SAS/IML function that takes several arguments. Some of the arguments have default values. When the module is called, I want to compute some quantity, but I only want to compute it for the […]

Post a Comment ## Compute the *k*th smallest data value in SAS

A SAS programmer recently posted a question to the SAS/IML Support Community about how to compute the kth smallest value in a vector of numbers. In the DATA step, you can use the SMALLEST function to find the smallest value in an array, but there is no equivalent built-in function […]

Post a Comment ## Elementwise minimum and maximum operators

Like most programming languages, the SAS/IML language has many functions. However, the SAS/IML language also has quite a few operators. Operators can act on a matrix or on rows or columns of a matrix. They are less intuitive, but can be quite powerful because they enable you perform computations without […]

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