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Programming Tips

Rick WicklinJune 6, 2018 3

Sample and obtain the results in random order

The SURVEYSELECT procedure in SAS 9.4M5 supports the OUTRANDOM option, which causes the selected items in a simple random sample to be randomly permuted after they are selected. This article describes several statistical tasks that benefit from this option, including simulating card games, randomly permuting observations in a DATA step,

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Programming Tips

Rick WicklinJune 4, 2018 4

An easy way to make a "Top 10" table and bar chart in SAS

Years ago, I wrote an article about how to create a Top 10 table and bar chart. The program can be trivially modified to create a "Top N" table and plot, such as Top 5, Top 20, or even Top 100. Not long after the article was written, the developer

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Learn SAS | Programming Tips

Rick WicklinMay 29, 2018 14

6 easy ways to specify a list of variables in SAS

The SAS language provides syntax that enables you to quickly specify a list of variables. SAS statements that accept variable lists include the KEEP and DROP statements, the ARRAY statement, and the OF operator for comma-separated arguments to some functions. You can also use variable lists on the VAR statements

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Programming Tips

Rick WicklinMay 21, 2018 1

Position items in a grid

In a recent blog post, Chris Hemedinger used a scatter plot to show the result of 100 coin tosses. Chris arranged the 100 results in a 10 x 10 grid, where the first 10 results were shown on the first row, the second 10 were shown on the second row, and so

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Analytics | Programming Tips

Rick WicklinMay 9, 2018 0

Independent streams of random numbers in SAS

In a previous blog post, I discussed ways to produce statistically independent samples from a random number generator (RNG). The best way is to generate all samples from one stream. However, if your program uses two or more SAS DATA steps to simulate the data, you cannot use the same

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Programming Tips

Rick WicklinMay 7, 2018 0

Independence and overlap in streams of random numbers

Simulation studies require both randomness and reproducibility, two qualities that are sometimes at odds with each other. A Monte Carlo simulation might need to generate millions of random samples, where each sample contains dozens of continuous variables and many thousands of observations. In simulation studies, the researcher wants each sample

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Analytics | Programming Tips

Rick WicklinApril 25, 2018 0

An easier way to run thousands of regressions

SAS programmers on SAS discussion forums sometimes ask how to run thousands of regressions of the form Y = B0 + B1*X_i, where i=1,2,.... A similar question asks how to solve thousands of regressions of the form Y_i = B0 + B1*X for thousands of response variables. I have previously

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Programming Tips

Rick WicklinApril 18, 2018 3

The sweep operator: A fundamental operation in regression

The sweep operator performs elementary row operations on a system of linear equations. The sweep operator enables you to build regression models by "sweeping in" or "sweeping out" particular rows of the X`X matrix. As you do so, the estimates for the regression coefficients, the error sum of squares, and

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Programming Tips

Rick WicklinApril 16, 2018 0

Random permutations without duplicates

A colleague and I recently discussed how to generate random permutations without encountering duplicates. Given a set of n items, there are n! permutations My colleague wants to generate k unique permutations at random from among the total of n!. Said differently, he wants to sample without replacement from the

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Learn SAS | Programming Tips

Rick WicklinApril 11, 2018 4

Find the unique rows of a numeric matrix

Sometimes it is important to ensure that a matrix has unique rows. When the data are all numeric, there is an easy way to detect (and delete!) duplicate rows in a matrix. The main idea is to subtract one row from another. Start with the first row and subtract it

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