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Rick WicklinOctober 9, 2023 1

Functions for continuous probability distributions in SAS

The documentation for Python's SciPy package provides a table that concisely summarizes functions that are associated with continuous probability distributions. This article provides a similar table for SAS functions. For more information on the CDF, PDF, quantile, and random-variate functions, see "Four essential functions for statistical programmers." SAS functions for

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Learn SAS | Programming Tips

Rick WicklinOctober 4, 2023 0

Use design matrices to analyze subgroups in SAS IML

A previous article shows ways to perform efficient BY-group processing in the SAS IML language. BY-group processing is a SAS-ism for what other languages call group processing or subgroup processing. The main idea is that the data set contains several discrete variables such as sex, race, education level, and so

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Programming Tips

Rick WicklinSeptember 25, 2023 0

Define or extract the diagonals of a matrix

Many useful matrices in applied math and statistics have a banded structure. Examples include diagonal matrices, tridiagonal matrices, banded matrices, and Toeplitz matrices. An example of an unsymmetric Toeplitz matrix is shown to the right. Notice that the matrix is constant along each diagonal, including sub- and superdiagonals. Recently, I

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Data Visualization | Programming Tips

Rick WicklinSeptember 20, 2023 1

Avoid domain errors by using Taylor series

The other day I was trying to numerically integrate the function f(x) = sin(x)/x on the domain [0,∞). The graph of this function is shown to the right. In SAS, you can use the QUAD subroutine in SAS IML software to perform numerical integration. Some numerical integrators have difficulty computing

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Data Visualization | Learn SAS | Programming Tips

Rick WicklinSeptember 18, 2023 2

Use PROC SGPLOT to embed a graph inside another graph

Did you know that you can embed one graph inside another by using PROC SGPLOT in SAS? A typical example is shown to the right. The large graph shows kernel density estimates for the distribution of the Cholesterol variable among male and female patients in a heart study. The small

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Learn SAS | Programming Tips

Rick WicklinSeptember 13, 2023 0

The SG annotation macros in SAS

I don't often use the SG annotation facility in SAS for adding annotations to statistical graphics, but when I do, I enjoy the convenience of the SG annotation macros. I can never remember the details of the SG annotation commands, but I know that the SG annotation macros will create

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Learn SAS | Programming Tips

Rick WicklinSeptember 11, 2023 1

On the performance of BY-group processing in SAS IML

Many SAS procedures support a BY statement that enables you to perform an analysis for each unique value of a BY-group variable. The SAS IML language does not support a BY statement, but you can program a loop that iterates over all BY groups. You can emulate BY-group processing by

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Analytics | Learn SAS | Programming Tips

Rick WicklinSeptember 6, 2023 7

Model data from published summary statistics

There are many ways to model a set of raw data by using a continuous probability distribution. It can be challenging, however, to choose the distribution that best models the data. Are the data normal? Lognormal? Is there a theoretical reason to prefer one distribution over another? The SAS has

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Learn SAS | Programming Tips

Rick WicklinAugust 30, 2023 2

Simulate the use of personal checks in the US

Does anyone write paper checks anymore? According to researchers at the Federal Reserve Bank of Atlanta (Greene, et al., 2020), the use of paper checks has declined 63% among US consumers since the year 2000. The researchers surveyed more than 3,000 consumers in 2017-2018 and discovered that only 7% of

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Analytics | Data Visualization | Programming Tips

Rick WicklinAugust 28, 2023 6

Generate random uniform points in an ellipse

I have previously written about how to efficiently generate points uniformly at random inside a sphere (often called a ball by mathematicians). The method uses a mathematical fact from multivariate statistics: If X is drawn from the uncorrelated multivariate normal distribution in dimensiond, then S = r*X / ||X|| has

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