Monthly Archives: July 2009

Beautiful Data

July 27, 2009
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Beautiful Data

O'Reilly's recent publication Beautiful Data has a chapter by Jeff Jonas which is enough reason in itself for me to recommend it. The chapter, Data Finds Data, is also available as a PDF download.

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R Snippet for Sampling from a Dataframe

July 27, 2009
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It took me a while to figure this out, so I thought I'd share. I have a dataframe with millions of observations in it, and I want to estimate a density distribution, which is a memory intensive process. Running my kde2d function on the full dataframe throws and error -- R tries to allocate a vector that...

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biomaRt

July 27, 2009
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I use R and Bioconductor for most of my work. I am also increasingly replacing things I would have done before in Perl with R. One such example of this is the Bioconductor module biomaRt.As the name suggest it allows for access to BioMart via R. BioMart is a method of accessing large online databases...

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Book now shipping from Amazon

July 27, 2009
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Book now shipping from Amazon

Amazon now reports that the book is in stock! The current discount is 13%.Or, order from the publisher. If you are an ASA member, you can use the online discount code 634LH to obtain a 15% discount.

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Paired Student’s t-test

July 26, 2009
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Paired Student’s t-test

Comparison of the means of two sets of paired samples, taken from two populations with unknown variance.A school athletics has taken a new instructor, and want to test the effectiveness of the new type of training proposed by comparing the average time...

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Select operations on R data frames

July 26, 2009
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Select operations on R data frames

The R language is weird - particularly for those coming from a typical programmer's background, which likely includes OO languages in the curly-brace family and relational databases using SQL. A key data structure in R, the data.frame, is used somethin...

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Rosetta Code

July 26, 2009
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Rosetta Code

Today I'd like to suggest the interesting Rosetta Code site:Rosetta Code is a programming chrestomathy site. The idea is to present solutions to the same task in as many different languages as possible, to demonstrate how languages are similar and diff...

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Two sample Student’s t-test #2

July 25, 2009
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Two sample Student’s t-test #2

Comparison of the averages of two independent groups, extracted from two populations at variance unknown; sample variances are not homogeneous.We want to compare the heights in inches of two groups of individuals. Here the measurements:A: 175, 168, 168...

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Example 7.7: Tabulate binomial probabilities

July 25, 2009
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Example 7.7: Tabulate binomial probabilities

Suppose we wanted to assess the probability P(X=x) for a binomial random variate with n = 10 and with p = .81, .84, ..., .99. This could be helpful, for example, in various game settings. In SAS, we find the probability that X=x using differences in t...

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Two sample Student’s t-test #1

July 24, 2009
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Two sample Student’s t-test #1

t-Test to compare the means of two groups under the assumption that both samples are random, independent, and come from normally distributed population with unknow but equal variancesHere I will use the same data just seen in a previous post. The data ...

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