SAS software provides many run-time functions that you can call from your SAS/IML or DATA step programs. The SAS/IML language has several hundred built-in statistical functions, and Base SAS software contains hundreds more. However, it is common for statistical programmers to extend the run-time library to include special user-defined functions.
Last week I blogged about how to construct a smoother for a time series for the temperature in Albany, NY from 1995 to March, 2012. I smoothed the data by "folding" the time series into a single "year" that contains repeated measurements for each day of the year. Experts in
In yesterday's post, I discussed a "quick and dirty" method to smooth periodic data. However, after I smoothed the data I remarked that the smoother itself was not exactly periodic. At the end points of the periodic interval, the smoother did not have equal slopes and the method does not
Over at the SAS and R blog, Ken Kleinman discussed using polar coordinates to plot time series data for multiple years. The time series plot was reproduced in SAS by my colleague Robert Allison. The idea of plotting periodic data on a circle is not new. In fact it goes
Over at the SAS Discussion Forums, someone asked how to use SAS to fit a Poisson distribution to data. The questioner asked how to fit the distribution but also how to overlay the fitted density on the data and to create a quantile-quantile (Q-Q) plot. The questioner mentioned that the
Locating missing values is important in statistical data analysis. I've previously written about how to count the number of missing values for each variable in a data set. In Base SAS, I showed how to use the MEANS or FREQ procedures to count missing values. In the SAS/IML language, I
Earlier this week I described a common programming pattern in the SAS macro language. The pattern sets up a loop for processing each distinct value of a classification variable. The program uses the PROC SQL SELECT INTO feature to populate SAS macro variables. The effect: you can roll your own
How to write a SAS macro program to repeat your SAS processing for each value of a BY grouping variable.
In the United States, this upcoming weekend is when we turn our clocks forward one hour as we adopt daylight saving time. (Some people will also flip their mattresses this weekend!) Daylight saving time (DST) in the US begins on the second Sunday in March and ends on the first
About once a month, a customer approaches SAS and asks a question of significance. By "significance", I don't necessarily mean "of great importance", but instead I mean "of how SAS handles large numbers, or floating-point values with many significant digits". In response, we always first ask why they asked. This
The SAS DATA step supports a special syntax for determining whether a value is contained in an interval: y = (-2 < x < 2); This expression creates an indicator variable with the value 1 if x is in the interval (-2,2) and 0 otherwise. There is not a standard
As SAS user Marje Fecht said "We all want a 'SAS programming assistant' to help us complete our jobs more quickly." Fecht, Senior Partner at Prowerk Consulting, then went on to say "In her book SAS Macro Programming Made Easy, Second Edition, Michele Burlew encourages us to take advantage of the SAS
Have you ever wanted to run a sample program from the SAS documentation or wanted to use a data set that appears in the SAS documentation? You can: all programs and data sets in the documentation are distributed with SAS, you just have to know where to look! Sample data
The other day I encountered the following SAS DATA step for generating three normally distributed variables. Study it, and see if you can discover what is unnecessary (and misleading!) about this program: data points; drop i; do i=1 to 10; x=rannor(34343); y=rannor(12345); z=rannor(54321); output; end; run; The program creates the
So many of us struggle with this mountain. In fact, 68.27% of us get within sight of reaching the summit (while 95.47% of us are at least on a perceivable slope). We run, walk, crawl and sometimes slide our way uphill (from one direction or the other) until we finally
Statistical programmers often need mathematical constants such as π (3.14159...) and e (2.71828...). Programmers of numerical algorithms often need to know machine-specific constants such as the machine precision constant (2.22E-16 on my Windows PC) or the largest representable double-precision value (1.798E308 on my Windows PC). Some computer languages build these
In the immortal words of Britney Spears: Oops! I did it again. At least, I'm afraid that I did. I think I might have helped a SAS student with a homework assignment, or perhaps provided an answer in preparation for a SAS certification exam. Or maybe it was a legitimate
On the heels of the release of the popular SAS macro variable viewer from last month, I'm providing another custom task that I hope will prove just as useful. This one is a SAS options viewer, similar in concept to the OPTIONS window in SAS display manager. You can download
This week's SAS author's tip comes from Jack Shostak - manager of statistical programming at the Duke Clinical Research Institute. Despite his youthful appearance, Jack's been using SAS since 1985 and is the author of SAS Programming in the Pharmaceutical Industry and coauthor of Common Statistical Methods for Clinical Research with SAS Examples,
A few colleagues and I were exchanging short snippets of SAS code that create Christmas trees and other holiday items by using the SAS DATA step to arrange ASCII characters. For example, the following DATA step (contributed by Udo Sglavo) creates a Christmas tree with ornaments and lights: data _null_;
Rick posted a tip today about using abbreviations in the SAS program editor window (often referred to as the "enhanced editor"). Defining abbreviations is a great way to save keystrokes and re-use "templates" of code that you've squirreled away. (One of Rick's readers also picked up on the tip, and
I've been working with date-time data on a recent project, and I've come across a few SAS programs that have "opportunity for improvement" when it comes time to create reports. (Or maybe I haven't, and I contrived this entire blog post so that I could reference one of my favorite
SAS programming is taught in schools all over the world, including in high schools. Occasionally, I receive questions via my blog such as this one: Can somebody help me on this? Write a short DATA _NULL_ step to determine the largest integer you can store on your computer in 3,
Sometimes a population of individuals is modeled as a combination of subpopulations. For example, if you want to model the heights of individuals, you might first model the heights of males and females separately. The height of the population can then be modeled as a combination of the male and
The other day I encountered a SAS Knowledge Base article that shows how to count the number of missing and nonmissing values for each variable in a data set. However, the code is a complicated macro that is difficult for a beginning SAS programmer to understand. (Well, it was hard
Looping is essential to statistical programming. Whether you need to iterate over parameters in an algorithm or indices in an array, a loop is often one of the first programming constructs that a beginning programmer learns. Today is the first anniversary of this blog, which is named The DO Loop,
I previously showed how to generate random numbers in SAS by using the RAND function in the DATA step or by using the RANDGEN subroutine in SAS/IML software. These functions generate a stream of random numbers. (In statistics, the random numbers are usually a sample from a distribution such as
One of the highly visible changes in SAS 9.3 is the fact that the old LISTING destination is no longer the default destination for ODS output. Instead, the HTML destination is the default. One positive consequence of this is that ODS graphics and tables are interlaced in the output. Another
Exploring correlation between variables is an important part of exploratory data analysis. Before you start to model data, it is a good idea to visualize how variables related to one another. Zach Mayer, on his Modern Toolmaking blog, posted code that shows how to display and visualize correlations in R.
You can generate a set of random numbers in SAS that are uniformly distributed by using the RAND function in the DATA step or by using the RANDGEN subroutine in SAS/IML software. (These same functions also generate random numbers from other common distributions such as binomial and normal.) The syntax
