Blogs

Blogs

Tag: Tips and Techniques

Rick WicklinOctober 14, 2011 0

Optimizing? Two hints for specifying derivatives

I previously wrote about using SAS/IML for nonlinear optimization, and demonstrated optimization by maximizing a likelihood function. Many well-known optimization algorithms require derivative information during the optimization, including the conjugate gradient method (implemented in the NLPCG subroutine) and the Newton-Raphson method (implemented in the NLPNRA method). You should specify analytic

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Rick WicklinOctober 10, 2011 0

SAS/IML tip sheets

To celebrate the first anniversary of Statistical Programming with SAS/IML Software, you can now download the SAS/IML tip sheets (also called "cheat sheets") that I created for the book. At conferences, SAS Press displays these tip sheets next to my book. They have been very popular. Download these SAS/IML cheat

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Rick WicklinSeptember 26, 2011 0

Using the MOD function as a debugging tool

I showed a SAS/IML customer a debugging tip, and she said that I should blog about it because she had never seen it before. The tip is very simple: inside of a DO loop, use the MOD function to selectively print the values of variables. Recall that the expression MOD(a,b)

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Rick WicklinJuly 25, 2011 0

A simple signum function

The other day I needed to compute the signum function for each element of a matrix. If x is a real number, then the sgn(x) is -1 when x<0, 1 when x>0, and 0 when x=0. I wrote a SAS/IML module that contains a compact little expression: proc iml; start

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Rick WicklinJuly 15, 2011 0

Five new features of SAS 9.3 for statistical programmers

Welcome, SAS 9.3! I've already blogged about some interface and graphical changes that everyone should know about. Now I'll put on my statistical hat and mention a few 9.3 features that excite me, personally, as a data analyst and a statistical programmer: As a statistician, I am keen to try

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Rick WicklinJuly 14, 2011 0

Welcome SAS 9.3! Five interface and graphics features that everyone can use

Here are a few new interface and graphics changes that every SAS programmer should know about SAS 9.3: HTML is now the default output destination when you run the SAS windowing environment. This means that tables and graphs appear in an HTML document instead of the classic LISTING destination. Of

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Rick WicklinJune 29, 2011 0

Add a diagonal line to a scatter plot

In my statistical analysis of coupons article, I presented a scatter plot that includes the identity line, y=x. This post describes how to write a general program that uses the SGPLOT procedure in SAS 9.2. By a "general program," I mean that the program produces the result based on the

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Rick WicklinMay 17, 2011 0

Inadequate finishes

Andrew Ratcliffe posted a fine article titled "Inadequate Mends" in which he extols the benefits of including the name of a macro on the %MEND statement. That is, if you create a macro function named foo, he recommends that you include the name in two places: %macro foo(x); /** define

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Rick WicklinMay 16, 2011 0

Finding data that satisfy a criterion

A fundamental operation in data analysis is finding data that satisfy some criterion. How many people are older than 85? What are the phone numbers of the voters who are registered Democrats? These questions are examples of locating data with certain properties or characteristics. The SAS DATA step has a

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Rick WicklinMay 2, 2011 0

Sequential access: Reading one observation at a time in SAS/IML software

The most common way to read observations from a SAS data set into SAS/IML matrices is to read all of the data at once by using the ALL clause in the READ statement. However, the READ statement also has options that do not require holding all of the observations in

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Rick WicklinApril 4, 2011 0

How to sample from independent normal distributions

In my article on computing confidence intervals for rankings, I had to generate p random vectors that each contained N random numbers. Each vector was generated from normal distribution with different parameters. This post compares two different ways to generate p vectors that are sampled from independent normal distributions. Sampling

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Rick WicklinMarch 23, 2011 0

Indirect assignment: How to create and use matrices named x1, x2,..., xn

I recently blogged about how to eliminate a macro loop in favor of using SAS/IML language statements. The purpose of the program was to extract N 3x3 matrices from a big 3Nx3 matrix. The main portion of my PROC IML program looked something like this: proc iml; ... do i=0

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Rick WicklinMarch 7, 2011 0

Need case-insensitive string comparisons? UPCASE!

String comparisons in SAS software are case-sensitive. For example, the uppercase letter "F" and lowercase letter "f" are treated as unique characters. When these two letters represent the same condition (for example, a female patient), the strings need to be handled in a case-insensitive manner, and a SAS programmer might

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Rick WicklinFebruary 28, 2011 0

Simulation and sampling in Las Vegas

If you haven't signed up for SAS Global Forum 2011 in Las Vegas, you'd better get moving: February 28 is the last day for early registration and the discounted hotel prices. You should also sign up for the pre-conference statistical tutorials, which are filling up fast! I was tempted to

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Rick WicklinJanuary 24, 2011 0

Test whether a sequence is increasing

The other day I needed to check that a sequence of numerical values was in strictly increasing order. My first thought was to sort the values and compare the sorted and original values, but I quickly discarded that approach because it does not detect duplicate values in a montonic (nondecreasing)

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Rick WicklinDecember 20, 2010 0

Readers' choice 2010: The DO Loop's most-read posts

When I wake up early to write my blog, I often wonder, "Is anyone going to read this?" Apparently so. I started writing The DO Loop in September, 2010. Since then, I've posted about 60 entries about statistical programming with SAS/IML software. Since this is a statistical blog, it is

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Rick WicklinDecember 13, 2010 0

How to find and fix programming errors

NOTE: SAS stopped shipping the SAS/IML Studio interface in 2018. The references in this article to IMLPlus and SAS/IML Studio are no longer relevant. There are three kinds of programming errors: parse-time errors, run-time errors, and logical errors. It doesn't matter what language you are using (SAS/IML, MATLAB, R, C/C++,

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Rick WicklinDecember 6, 2010 0

Shorthand notation for row and column operations

The SAS/IML language enables you to perform matrix-vector computations. However, it also provides a convenient "shorthand notation" that enables you to perform elementwise operation on rows or columns in a natural way. You might know that the SAS/IML language supports subscript reduction operators to compute basic rowwise or columnwise quantities.

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Rick WicklinNovember 29, 2010 0

How to interpret SAS/IML error messages

Errors. We all make them. After all, “to err is human.” Or, as programmers often say, “To err is human, but to really foul things up requires a computer” (Farmer’s Almanac, 1978). This post describes how to interpret error messages from PROC IML that appear in the SAS log. The

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Rick WicklinNovember 15, 2010 0

Free chapter: Getting Started with SAS/IML

I am pleased to announce that the fine folks at SAS Press have made Chapter 2 of my book, Statistical Programming with SAS/IML Software available as a free PDF document. The chapter is titled "Getting Started with the SAS/IML Matrix Programming Language," and it features More than 60 fully functional

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Rick WicklinNovember 8, 2010 0

Free webinar on SAS/IML Studio

I just got back from a great conference in San Diego at the 2010 meeting of the Western Users of SAS Software (WUSS) where I gave several presentations on PROC IML and SAS/IML Studio. If you didn't make it to San Diego, you can still read my 2010 paper on

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Rick WicklinNovember 3, 2010 0

SAS/IML software featured at WUSS

Today I'm in San Diego at the 2010 meeting of the Western Users of SAS Software (WUSS). I am giving several presentations on SAS/IML and SAS/IML Studio: A tutorial workshop on SAS/IML Studio for the SAS/STAT User. The material in this tutorial is a small sampling of Chapters 4–11 of

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Rick WicklinNovember 1, 2010 0

Tips and techniques - What’s the difference?

In this blog and in the book Statistical Programming with SAS/IML Software, I present tips and techniques for writing efficient SAS/IML programs for data analysis, simulation, matrix computations, and other topics of interest to statistical programmers. When I was writing my book, one of the reviewers commented that he wasn’t

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Rick WicklinOctober 29, 2010 0

Tricks and Treats

How can you change a programming trick into a programming treat? Try this algorithm: If you develop a clever snippet of code, squirrel it away. This snippet is a "trick." If you use the trick a second time, copy and modify the code. The trick has become a "treat." If

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Rick WicklinOctober 13, 2010 0

Generate all permutations in SAS

In a previous post, I discussed how to generate random permutations of N elements. But what if you want to systematically iterate through a list of ALL permutations of N elements? In the SAS DATA step you can use the ALLPERM subroutine in the SAS DATA step. For example, the

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Rick WicklinSeptember 22, 2010 0

Efficient Sampling

Recently, SAS Global Forum announced the call for papers for the 2011 conference to be held at Caesars Palace in Las Vegas. Since the conference is in Las Vegas, I’ve been thinking a lot about games of chance: blackjack, craps, roulette, and the like. You can analyze these games by

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Rick WicklinSeptember 20, 2010 0

Five Reasons to CLOSE Your Data Sets

My mother taught me to put things away when I'm finished using them. She doesn't use a computer, but if she did, I know that she'd approve of this tip from my book: Tip: Always close your files and data sets when you are finished reading or writing them. In

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