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Programming Tips

Rick WicklinMay 8, 2017 3

Quick! What is the next term in the numerical sequence 1, 2, 1, 2, 3, 4, 5, 4, 3, 4, ...? If you said '3', then you must be an American history expert, because that sequence represents the number of living US presidents beginning with Washington's inauguration on 30APR1789 and

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Analytics | Data Visualization | Programming Tips

Rick WicklinApril 26, 2017 0

Visualize a design matrix

Most SAS regression procedures support a CLASS statement which internally generates dummy variables for categorical variables. I have previously described what dummy variables are and how are they used. I have also written about how to create design matrices that contain dummy variables in SAS, and in particular how to

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Advanced Analytics | Learn SAS | Programming Tips

Rick WicklinApril 19, 2017 50

Regression with restricted cubic splines in SAS

Restricted cubic splines are a powerful technique for modeling nonlinear relationships by using linear regression models. I have attended multiple SAS Global Forum presentations that show how to use restricted cubic splines in SAS regression procedures. However, the presenters have all used the %RCSPLINE macro (Frank Harrell, 1988) to generate

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Analytics | Programming Tips

Optimal value of quadratic function of two variables

Rick WicklinApril 12, 2017 3

Quadratic optimization in SAS

At SAS Global Forum last week, I saw a poster that used SAS/IML to optimized a quadratic objective function that arises in financial portfolio management (Xia, Eberhardt, and Kastin, 2017). The authors used the Newton-Raphson optimizer (NLPNRA routine) in SAS/IML to optimize a hypothetical portfolio of assets. The Newton-Raphson algorithm

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Programming Tips

Rick WicklinApril 10, 2017 0

A simple trick to construct symmetric intervals

Many intervals in statistics have the form p ± δ, where p is a point estimate and δ is the radius (or half-width) of the interval. (For example, many two-sided confidence intervals have this form, where δ is proportional to the standard error.) Many years ago I wrote an article

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Programming Tips

Rick WicklinApril 5, 2017 11

Piecewise regression models and spline effects

Most regression models try to model a response variable by using a smooth function of the explanatory variables. However, if the data are generated from some nonsmooth process, then it makes sense to use a regression function that is not smooth. A simple way to model a discontinuous process in

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Programming Tips

Rick WicklinApril 3, 2017 6

Print tables in SAS/IML

One of the advantages of the new mixed-type tables in SAS/IML 14.2 (released with SAS 9.4m4) is the greatly enhanced printing functionality. You can control which rows and columns are printed, specify formats for individual columns, and even use templates to completely customize how tables are printed. Printing a table

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Programming Tips

SAS/IML lists can store objects of different shapes and sizes

Rick WicklinMarch 29, 2017 9

Lists: Nonmatrix data structures in SAS/IML

Lists are collections of objects. SAS/IML 14.2 supports lists as a way to store matrices, data tables, and other lists in a single object that you can pass to functions. SAS/IML lists automatically grow if you add new items to them and shrink if you remove items. You can also

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Programming Tips

Rick WicklinMarch 27, 2017 4

Is ODS graphics enabled? Use automatic macro variables to determine the state of SAS

Did you know that you can check a SAS macro variable to see if ODS graphics is enabled? The other day I wanted to write a SAS program that creates a graph only if ODS graphics is enabled. The solution is to check the SYSODSGRAPHICS macro variable, which is automatically

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Programming Tips

Rick WicklinMarch 22, 2017 3

Data tables: Nonmatrix data structures in SAS/IML

Prior to SAS/IML 14.2, every variable in the Interactive Matrix Language (IML) represented a matrix. That changed when SAS/IML 14.2 (released with SAS 9.4m4) introduced two new data structures: data tables and lists. This article gives an overview of data tables. I will blog about lists in a separate article.

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