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Rick WicklinJanuary 9, 2023 0

Since 2008, SAS has supported an interface for calling R from the SAS/IML matrix language. Many years ago, I wrote blog posts that describe how to call R from PROC IML. For SAS 9.4, the process of installing R and calling R from PROC IML is documented in the SAS/IML

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Analytics | Learn SAS | Programming Tips

Rick WicklinJanuary 4, 2023 0

Top 10 posts from The DO Loop in 2022

Last year, I wrote almost 90 articles for The DO Loop blog. My most popular articles were about SAS programming, data visualization, statistics and data analysis, and matrix computations. If you missed these articles when I published them—or if you want to read them again!— here is the "Reader's Choice

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Analytics | Learn SAS | Programming Tips

Rick WicklinDecember 14, 2022 0

Construct heterogeneous structured covariance matrices in SAS

A previous article describes how to use SAS IML software to construct common covariance structures that are encountered in mixed models. Each covariance matrix has several parameters, and you want to construct a matrix for any choice of the parameters. After you have constructed the covariance matrix, you can use

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Analytics | Programming Tips

Rick WicklinNovember 21, 2022 0

The area under a piecewise linear curve

Recently, I needed to know "how much" of a piecewise linear curve is below the X axis. The coordinates of the curve were given as a set of ordered pairs (x1,y1), (x2,y2), ..., (xn, yn). The question is vague, so the first step is to define the question better. Should

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Analytics | Data Visualization | Programming Tips

Rick WicklinNovember 16, 2022 3

Optimal linear profile plots in SAS

A profile plot is a way to display multivariate values for many subjects. The optimal linear profile plot was introduced by John Hartigan in his book Clustering Algorithms (1975). In Michael Friendly's book (SAS System for Statistical Graphics, 1991), Friendly shows how to construct an optimal linear profile by using

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Analytics | Data Visualization | Learn SAS | Programming Tips

Rick WicklinNovember 7, 2022 0

The area of the convex hull of random points

I recently blogged about how to compute the area of the convex hull of a set of planar points. This article discusses the expected value of the area of the convex hull for n random uniform points in the unit square. The article introduces an exact formula (due to Buchta,

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Analytics | Learn SAS | Programming Tips

Rick WicklinNovember 2, 2022 0

The area and perimeter of a convex hull

The area of a convex hull enables you to estimate the area of a compact region from a set of discrete observations. For example, a biologist might have multiple sightings of a wolf pack and want to use the convex hull to estimate the area of the wolves' territory. A

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Analytics | Data Visualization | Learn SAS

Rick WicklinOctober 26, 2022 2

Visualize dependencies of missing values

A SAS programmer asked how to create a graph that shows whether missing values in one variable are associated with certain values of another variable. For example, a patient who is supposed to monitor his blood glucose daily might have more missing measurements near holidays and in the summer months

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Analytics | Learn SAS | Programming Tips

Rick WicklinOctober 24, 2022 3

Implement binary logistic regression from first principles

I recently gave a presentation about the SAS/IML matrix language in which I emphasized that a matrix language enables you to write complex analyses by using only a few lines of code. In the presentation, I used least squares regression as an example. One participant asked how many additional lines

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Analytics | Learn SAS | Programming Tips

Rick WicklinOctober 19, 2022 0

On solving rank-deficient systems of equations in SAS

Recently, I needed to write a program that can provide a solution to a regression-type problem, even when the data are degenerate. Mathematically, the problem is an overdetermined linear system of equations X*b = y, where X is an n x p design matrix and y is an n x 1 vector. For most

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