## Tag: Tips and Techniques

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Submatrices of matrices

Have you ever seen the "brain teaser" for children that shows a 4 x 4 grid and asks "how many squares of any size are in this grid?" To solve this problem, the reader must recognize that there are sixteen 1 x 1 squares, nine 2 x 2 squares, four 3 x 3 squares, and one 4 x 4 square.

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Top posts from The DO Loop in 2019

Last year, I wrote more than 100 posts for The DO Loop blog. The most popular articles were about SAS programming tips for data analysis, statistical analysis, and data visualization. Here are the most popular articles from 2019 in each category. SAS programming tips Create training, testing, and validation data

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Compute the first or last day of a month or year

Every year at Halloween, I post an article that shows a SAS trick that is a real treat. This article shows how to use the INTNX function to find dates that are related to a specified date. The INTNX function is a sweet treat, indeed. I previously wrote an article

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Use regular expressions to specify variable names in SAS

A common task in SAS programming is to specify a list of variables that satisfy some pattern. You can specify lists for the KEEP= or DROP= data set options, and you can use lists of variables on many SAS statements such as the VAR and MODEL statements. Although SAS has

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The essential guide to binning in SAS

Do you want to bin a numeric variable into a small number of discrete groups? This article compiles a dozen resources and examples related to binning a continuous variable. The examples show both equal-width binning and quantile binning. In addition to standard one-dimensional techniques, this article also discusses various techniques

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Write to a SAS data set from inside a SAS/IML loop

In SAS/IML programs, a common task is to write values in a matrix to a SAS data set. For some programs, the values you want to write are in a matrix and you use the CREATE FROM/APPEND FROM syntax to create the data set, as follows: proc iml; X =

Programming Tips
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Efficient evaluation of a quadratic form

A quadratic form is a second-degree polynomial that does not have any linear or constant terms. For multivariate polynomials, you can quickly evaluate a quadratic form by using the matrix expression x` A x This computation is straightforward in a matrix language such as SAS/IML. However, some computations in statistics

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Convergence in mixed models: When the estimated G matrix is not positive definite

I've previously written about how to deal with nonconvergence when fitting generalized linear regression models. Most generalized linear and mixed models use an iterative optimization process, such as maximum likelihood estimation, to fit parameters. The optimization might not converge, either because the initial guess is poor or because the model

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10 posts from 2018 that deserve a second look

Numbers don't lie, but sometimes they don't reveal the full story. Last week I wrote about the most popular articles from The DO Loop in 2018. The popular articles are inevitably about elementary topics in SAS programming or statistics because those topics have broad appeal. However, I also write about

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Top posts from The DO Loop in 2018

Last year, I wrote more than 100 posts for The DO Loop blog. Of these, the most popular articles were about data visualization, SAS programming tips, and statistical data analysis. Here are the most popular articles from 2018 in each category. Data Visualization Visualize repetition in song lyrics: In one

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