# Blog Archives

## Importing an Excel Workbook into R

June 5, 2014
By

The usual route for importing data from spreadsheet applications like Excel or OpenOffice into R involves first exporting the data in CSV format. A newer (c. 2011) and more efficient CRAN package, called XLConnect, facilitates reading an entire Excel workbook and manipulating worksheets and cells programmatically from within R. XLConnect doesn't require a running installation of Microsoft Excel...

## Melbourne’s Weather and Cross Correlations

April 1, 2014
By

During a lunchtime discussion among recent GCaP class attendees, the topic of weather came up and I casually mentioned that the weather in Melbourne, Australia, can be very changeable because the continent is so old that there is very little geographical relief to moderate the prevailing winds coming from the west. In general, Melbourne is said to have...

## Facebook Meets Florence Nightingale and Enrico Fermi

February 19, 2014
By

Highlighting Facebook's mistakes and weaknesses is a popular sport. When you're the 800 lb gorilla of social networking, it's inevitable. The most recent rendition of FB bashing appeared in a serious study entitled, Epidemiological Modeling of Online Social Network Dynamics, authored by a couple of academics in the Department of Mechanical and Aerospace Engineering (???) at Princeton University. They...

## Response Time Percentiles for Multi-server Applications

December 25, 2013
By

In a previous post, I applied my rules-of-thumb for response time (RT) percentiles (or more accurately, residence time in queueing theory parlance), viz., 80th percentile: $R_{80}$, 90th percentile: $R_{90}$ and 95th percentile: $R_{95}$ to a cellphone application and found that the performance measurements were not completely consistent. Since the data appeared in a journal blog, I didn't...

## Laplace the Bayesianista and the Mass of Saturn

September 15, 2013
By

I'm reviewing Bayes' theorem and related topics for the upcoming GDAT class. In its simplest form, Bayes' theorem is statement about conditional probabilities. The probability of A, given that B has occurred, is expressed as: $$\Pr(A|B) = \dfrac{\Pr(B|A)\times\Pr(A)}{\Pr(B)} \label{eqn:bayes}$$ In Bayesian language, $\Pr(A|B)$ is called the posterior probability, $\Pr(A)$ the prior probability, and $\Pr(B|A)$ the likelihood. Bayes'...

## GDAT Class October 14-18, 2013

August 25, 2013
By

This is your fast track to enterprise performance analysis and capacity planning with an emphasis on applying R statistical tools to your performance data. Early-bird discounts are available for the Level III Guerrilla Data Analysis Techniques class O...

## Exponential Cache Behavior

May 15, 2013
By

Guerrilla alumnus Gary Little observed certain fixed-point behavior in simulations where disk IO blocks are updated randomly in a fixed size cache. For his python simulation with 10 million entries (corresponding to an allocation of about 400 MB of memory) the following results were obtained: Hit ratio (i.e., occupied) = 0.3676748 Miss ratio (i.e., inserts) = 0.6323252...

April 22, 2013
By

Pretty Damn Quick (PDQ) performs a mean value analysis of queueing network models: mean values in; mean values out. By mean, I mean statistical mean or average. Mean input values include such queueing metrics as service times and arrival rates. These could be sample means. Mean output values include such queueing metrics as waiting time and queue length. These...

## Upcoming GDAT Class May 6-10, 2013

April 22, 2013
By

Enrollments are still open for the Level III Guerrilla Data Analysis Techniques class to be held during the week May 6—10. Early-bird discounts are still available. Enquire when you register. As usual, all classes are held at our lovely Larkspur...

## Extracting the Epidemic Model: Going Beyond Florence Nightingale Part II

February 7, 2013
By

This is the second of a two part reexamination of Florence Nightingale's data visualization based on her innovative cam diagrams (my term) shown in Figure 1. Figure 1. Nightingale's original cam diagrams (click to enlarge)RecapIn Part I, I showed that FN applied sectoral areas, rather than a pie chart or conventional histogram, to reduce the visual impact of highly...