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Programming Tips

Rick WicklinApril 4, 2018 3

Distance correlation

Correlation is a statistic that measures how closely two variables are related to each other. The most popular definition of correlation is the Pearson product-moment correlation, which is a measurement of the linear relationship between two variables. Many textbooks stress the linear nature of the Pearson correlation and emphasize that

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Learn SAS | Programming Tips

Rick WicklinApril 2, 2018 5

The chi-square test: An example of working with rows and columns in SAS

As a general rule, when SAS programmers want to manipulate data row by row, they reach for the SAS DATA step. When the computation requires column statistics, the SQL procedure is also useful. When both row and column operations are required, the SAS/IML language is a powerful addition to a

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Analytics | Data Visualization | Programming Tips

Euclidean and L1 distances between observations and a target value for standardized data

Rick WicklinMarch 28, 2018 3

Find the distances between observations and a target value

Suppose you want to find observations in multivariate data that are closest to a numerical target value. For example, for the students in the Sashelp.Class data set, you might want to find the students whose (Age, Height, Weight) values are closest to the triplet (13, 62, 100). The way to

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Learn SAS | Programming Tips

Rick WicklinMarch 19, 2018 4

Compute with combinations: Maximize a function over combinations of variables

About once a month I see a question on the SAS Support Communities that involves what I like to call "computations with combinations." A typical question asks how to find k values (from a set of p values) that maximize or minimize some function, such as "I have 5 variables,

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Analytics | Programming Tips

Rick WicklinMarch 7, 2018 11

Fit a distribution from quantiles

Data analysts often fit a probability distribution to data. When you have access to the data, a common technique is to use maximum likelihood estimation (MLE) to compute the parameters of a distribution that are "most likely" to have produced the observed data. However, how can you fit a distribution

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Analytics | Programming Tips

Rick WicklinMarch 5, 2018 6

The probability of a saddle point in a matrix

Many people know that a surface can contain a saddle point, but did you know that you can define the saddle point of a matrix? Saddle points in matrices are somewhat rare, which means that if you choose a random matrix you are unlikely to choose one that has a

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Analytics | Programming Tips

Solve nonlinear system of equations in SAS

Rick WicklinFebruary 28, 2018 3

Solve a system of nonlinear equations with SAS

This article shows how to use SAS to solve a system of nonlinear equations. When there are n unknowns and n equations, this problem is equivalent to finding a multivariate root of a vector-valued function F(x) = 0 because you can always write the system as f1(x1, x2, ..., xn)

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Learn SAS | Programming Tips

Rick WicklinFebruary 26, 2018 8

How to use FIRST.variable and LAST.variable in a BY-group analysis in SAS

My article about the difference between CLASS variables and BY variables in SAS focused on SAS analytical procedures. However, the BY statement is also useful in the SAS DATA step where it is used to merge data sets and to analyze data at the group level. When you use the

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Analytics | Programming Tips

Quantiles are the solutions to the equation CDF(x)-p=0, where p is a probability

Rick WicklinFebruary 19, 2018 3

Compute the quantiles of any distribution

Your statistical software probably provides a function that computes quantiles of common probability distributions such as the normal, exponential, and beta distributions. Because there are infinitely many probability distributions, you might encounter a distribution for which a built-in quantile function is not implemented. No problem! This article shows how to

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Programming Tips

Rick WicklinFebruary 5, 2018 1

Simulate the birthday-matching problem

This article simulates the birthday-matching problem in SAS. The birthday-matching problem (also called the birthday problem or birthday paradox) answers the following question: "if there are N people in a room, what is the probability that at least two people share a birthday?" The birthday problem is famous because the

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