Blog Archives

Counting observations in two-dimensional bins

August 27, 2014
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Counting observations in two-dimensional bins

Last Monday I discussed how to choose the bin width and location for a histogram in SAS. The height of each histogram bar shows the number of observations in each bin. Although my recent article didn't mention it, you can also use the IML procedure to count the number of […]

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Choosing bins for histograms in SAS

August 25, 2014
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Choosing bins for histograms in SAS

When you create a histogram with statistical software, the software uses the data (including the sample size) to automatically choose the width and location of the histogram bins. The resulting histogram is an attempt to balance statistical considerations, such as estimating the underlying density, and "human considerations," such as choosing […]

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Analyzing activity-tracker data: How many steps per day do YOU take?

August 22, 2014
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Analyzing activity-tracker data: How many steps per day do YOU take?

My wife got one of those electronic activity trackers a few months ago and has been diligently walking every day since then. At the end of the day she sometimes reads off how many steps she walked, as measured by her activity tracker. I am always impressed at how many […]

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Creating heat maps in SAS/IML

August 20, 2014
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Creating heat maps in SAS/IML

In a previous blog post, I showed how to use the graph template language (GTL) in SAS to create heat maps with a continuous color ramp. SAS/IML 13.1 includes the HEATMAPCONT subroutine, which makes it easy to create heat maps with continuous color ramps from SAS/IML matrices. Typical usage includes […]

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Creating a basic heat map in SAS

August 18, 2014
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Creating a basic heat map in SAS

Heat maps have many uses. In a previous article, I showed how to use heat maps with a discrete color ramp to visualize matrices that have a small number of unique values, such as certain covariance matrices and sparse matrices. You can also use heat maps with a continuous color […]

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Guiding numerical integration: The PEAK= option in the SAS/IML QUAD subroutine

August 13, 2014
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Guiding numerical integration: The PEAK= option in the SAS/IML QUAD subroutine

One of the things I enjoy about blogging is that I often learn something new. Last week I wrote about how to optimize a function that is defined in terms of an integral. While developing the program in the article, I made some mistakes that generated SAS/IML error messages. By […]

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Ten tips for learning the SAS/IML language

August 11, 2014
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Ten tips for learning the SAS/IML language

A SAS customer wrote, "Now that I have access to PROC IML through the free SAS University Edition, what is the best way for me to learn to program in the SAS/IML language? How do I get started with PROC IML?" That is an excellent question, and I'm happy to […]

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Define an objective function that evaluates an integral in SAS

August 6, 2014
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Define an objective function that evaluates an integral in SAS

The SAS/IML language is used for many kinds of computations, but three important numerical tasks are integration, optimization, and root finding. Recently a SAS customer asked for help with a problem that involved all three tasks. The customer had an objective function that was defined in terms of an integral. […]

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Stigler’s seven pillars of statistical wisdom

August 5, 2014
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Stigler’s seven pillars of statistical wisdom

Wisdom has built her house; She has hewn out her seven pillars.      – Proverbs 9:1 At the 2014 Joint Statistical Meetings in Boston, Stephen Stigler gave the ASA President's Invited Address. In forty short minutes, Stigler laid out his response to the age-old question "What is statistics?" His answer was […]

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Reversing the limits of integration in SAS

August 4, 2014
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Reversing the limits of integration in SAS

In SAS software, you can use the QUAD subroutine in the SAS/IML language to evaluate definite integrals on an interval [a, b]. The integral is properly defined only for a < b, but mathematicians define the following convention, which enables you to make sense of reversing the limits of integration: […]

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