Blogs

Blogs

Advanced Analytics

Move beyond spreadsheets to data mining, forecasting, optimization – and more

Advanced Analytics

Rick WicklinMarch 11, 2011 0

Simulating a random walk

In my spare time, I enjoy browsing the StackOverflow discussion forum to see what questions people are asking about SAS, SAS/IML, and statistics. Last week, a statistics student asked for help with the following homework problem: I need to generate a one-dimensional random walk in which the step length and

Read More

Advanced Analytics

Rick WicklinMarch 9, 2011 0

Cuzick's Test for Trend: A case study in translating a MATLAB program into the SAS/IML language

Several times a year, I am contacted by a SAS account manager who tells me that a customer has asked whether it is possible to convert a MATLAB program to the SAS/IML language. Often the customer has an existing MATLAB program and wants to include the computation as part of

Read More

Advanced Analytics

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

Read More

Advanced Analytics

Rick WicklinMarch 4, 2011 0

How to use transparency to overcome overplotting

Do you have many points in your scatter plots that overlap each other? If so, your graph exhibits overplotting. Overplotting occurs when many points have similar coordinates. For example, the following scatter plot (which is produced by using the ODS statistical graphics procedure, SGPLOT) displays 12,000 points, many of which

Read More

Advanced Analytics

Rick WicklinMarch 2, 2011 0

The macro loop that vanished: How to simplify your SAS/IML programs

I don't use the SAS macro language very often. Because the SAS/IML language has statements for looping and evaluating expressions, I rarely write a macro function as part of a SAS/IML programs. Oh, sure, I use the %LET statement to define global constants, but I seldom use the %DO and

Read More

Advanced Analytics

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

Read More

Advanced Analytics

Mike GillilandFebruary 25, 2011 0

When Executive Managment Hurts

As we discussed last week, the forecasting process is often contaminated by individuals whose input makes the forecast worse. Sometimes this is intentional. For example, if I'm tired of hearing customers complain about out-of-stocks on retail shelves, I'll try to drive up the forecast so that more inventory will be

Read More

Advanced Analytics

Rick WicklinFebruary 25, 2011 0

Bias and covariance explained to an 11-year-old

I was inspired by Chris Hemedinger's blog posts about his daughter's science fair project. Explaining statistics to a pre-teenager can be a humbling experience. My 11-year-old son likes science. He recently set about trying to measure which of three projectile launchers is the most accurate. I think he wanted to

Read More

Advanced Analytics

Rick WicklinFebruary 23, 2011 0

SAS/IML operations compared with PROC SQL: Part 1

I don't know much about the SQL procedure, but I know that it is powerful. According to the SAS documentation for the SQL procedure, "PROC SQL can perform some of the operations that are provided by the DATA step and the PRINT, SORT, and SUMMARY procedures." Recently, a fellow blogger,

Read More

Advanced Analytics

Rick WicklinFebruary 21, 2011 0

How to build a vector from expressions

If you are a statistical programmer, sooner or later you have to compute a confidence interval. In the SAS/IML language, some beginning programmers struggle with forming a confidence interval. I don't mean that they struggle with the statistics (they know how to compute the relevant quantities), I mean that they

Read More

Advanced Analytics

Mike GillilandFebruary 18, 2011 0

Forecasting or Golf?

A recurring theme of The Business Forecasting Deal (both this blog and the book) is that forecasting is a huge waste of management time. This doesn't mean that forecasting is pointless, irrelevant, or entirely useless in running our organizations. It only means that the amount of time, money, and human

Read More

Advanced Analytics

Rick WicklinFebruary 18, 2011 0

Comedy vs. Drama: A comparative histogram of TV's top earners

The Flowing Data blog posted some data about how much TV actors get paid per episode. About a dozen folks have created various visualizations of the data (see the comments in the Flowing Data blog), several of them very glitzy and fancy. One variable in the data is a categorical

Read More

Advanced Analytics

Rick WicklinFebruary 16, 2011 0

Converting matrix subscripts to indices

Suppose that you want to create a matrix in SAS/IML software that has a special structure, such as a tridiagonal matrix. How do you do it? Or suppose that you want to find elements of a matrix A such that A[i,j] satisfies a certain condition. How do you get the

Read More

Advanced Analytics

Rick WicklinFebruary 14, 2011 0

A parametric view of love

If you tell my wife that she's married to a statistical geek, she'll nod knowingly. She is used to hearing sweet words of affection such as You are more beautiful than Euler's identity. or My love for you is like the exponential function: increasing, unbounded, and transcendental. But those are

Read More

Advanced Analytics

Mike GillilandFebruary 11, 2011 0

Guest Blogger: Len Tashman Previews Winter 2011 Issue of Foresight

The Winter 2011 issue of Foresight is now available. Here is Editor Len Tashman's preview: This issue of Foresight—our 20th since the journal’s genesis in 2005—begins with a new feature, Joe and Simon Sez. Joe is Joe Smith of Dean Foods and author of three valuable Foresight articles on forecast

Read More

Advanced Analytics

Rick WicklinFebruary 11, 2011 0

Scratch-off lottery Games: One way to design them

In a previous blog post, I described the rules for a tic-tac-toe scratch-off lottery game and showed that it is a bad idea to generate the game tickets by using a scheme that uses equal probabilities. Instead, cells that yield large cash awards must be assigned a small probability of

Read More

Advanced Analytics

Rick WicklinFebruary 10, 2011 0

Scratch-off lottery games: How NOT to design them

Because of this week's story about a geostatistician, Mohan Srivastava, who figured out how predict winning tickets in a scratch-off lottery, I've been thinking about scratch-off games. He discovered how to predict winners when he began to "wonder how they make these [games]." Each ticket has a set of "lucky

Read More

Advanced Analytics

Rick WicklinFebruary 9, 2011 0

Super Bowl pools and Roman numerals

I enjoyed the Dataists' data-driven blog on the best numbers to choose in a Super Bowl betting pool. It reminded me of my recent investigation of which initials are most common. Because the Dataists' blog featured an R function that converts Arabic numerals into Roman numerals, the blog post also

Read More

Advanced Analytics

Rick WicklinFebruary 9, 2011 0

Computing pairwise differences (efficiently, of course)

The other day, someone asked me how to compute a matrix of pairwise differences for a vector of values. The person asking the question was using SQL to do the computation for 2,000 data points, and it was taking many hours to compute the pairwise differences. He asked if SAS/IML

Read More

Advanced Analytics

Rick WicklinFebruary 7, 2011 0

How to use spatial statistics to crack a scratch-off game

On Friday, I posted an article about using spatial statistics to detect whether a pattern of points is truly random. That day, one of my colleagues asked me whether there are any practical applications of detecting spatial randomness or non-randomness. "Oh, sure," I replied, and rattled off a list of

Read More

Advanced Analytics

Rick WicklinFebruary 7, 2011 0

Passing arguments by reference: An efficient choice

When you pass a matrix as an parameter (argument) to a SAS/IML module, the SAS/IML language does not create a copy of the matrix. That approach, known as "calling by value," is inefficient. It is well-known that languages that implement call-by-value semantics suffer performance penalties. In the SAS/IML language, matrices

Read More

Advanced Analytics

Rick WicklinFebruary 4, 2011 0

Divide and count: A test for spatial randomness

Last week I generated two kinds of random point patterns: one from the uniform distribution on a two-dimensional rectangle, the other by jittering a regular grid by a small amount. My show choir director liked the second method (jittering) better because of the way it looks on stage: there are

Read More

Advanced Analytics

Rick WicklinFebruary 2, 2011 0

Count the number of points in 2D bins

One of my New Year's resolutions is to learn a new area of statistics. I'm off to a good start, because I recently investigated an issue which started me thinking about spatial statistics—a branch of statistics that I have never formally studied. During the investigation, I asked myself: Given an

Read More

Advanced Analytics

Rick WicklinJanuary 31, 2011 0

Reshaping data from wide to long format

As Cat Truxillo points out in her recent blog post, some SAS procedures require data to be in a "long" (as opposed to "wide") format. Cat uses a DATA step to convert the data from wide to long format. Although there is nothing wrong with this approach, I prefer to

Read More

Advanced Analytics

Rick WicklinJanuary 28, 2011 0

Random uniform versus uniformly spaced: Applying statistics to show choir

I sing in the SAS-sponsored VocalMotion show choir. It's like an adult version of Glee, except we have more pregnancies and fewer slushie attacks. For many musical numbers, the choreographer arranges the 20 performers on stage in an orderly manner, such as four rows of five singers. But every once

Read More

Advanced Analytics

Rick WicklinJanuary 26, 2011 0

Count the number of points in bins efficiently

A histogram displays the number of points that fall into a specified set of bins. This blog post shows how to efficiently compute a SAS/IML vector that contains those counts. I stress the word "efficiently" because, as is often the case, a SAS/IML programmer has a variety of ways to

Read More

Advanced Analytics

Rick WicklinJanuary 25, 2011 0

Computing 200 factorial: Using PROC IML as a really BIG calculator

Have you ever wanted to compute the exact value of a really big number such as 200! = 200*199*...*2*1? You can do it—if you're willing to put forth some programming effort. This blog post shows you how. Jiangtang Hu's recent blog discusses his quest to compute large factorials in many programming languages.

Read More

Advanced Analytics

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)

Read More

Advanced Analytics

Mike GillilandJanuary 21, 2011 0

Best Company to Work For -- Again

It has become routine. For the 14th straight time – which is every year since its first publication in 1998 – SAS has made the Fortune “100 Best Companies to Work For” list. This includes eight appearances in the top ten, and in 2011, for the second year in a

Read More

Advanced Analytics

Rick WicklinJanuary 21, 2011 0

How to create a grid of values?

In a previous post, I described ways to create SAS/IML vectors that contain uniformly spaced values. The methods did not involve writing any loops. This post describes how to perform a similar operation: creating evenly spaced values on a two-dimensional grid. The DATA step solution is simple, but an efficient

Read More

Previous 1 … 47 48 49 50 51 … 54 Next