July 2009

Kruskal-Wallis one-way analysis of variance

July 31, 2009 | Todos Logos

If you have to perform the comparison between multiple groups, but you can not run a ANOVA for multiple comparisons because the groups do not follow a normal distribution, you can use the Kruskal-Wallis test, which can be applied when you can not make ... [Read more...]

Analysis of variance: ANOVA, for multiple comparisons

July 30, 2009 | Todos Logos

Analysis of variance: ANOVA, for multiple comparisonsThe ANOVA model can be used to compare the mean of several groups with each other, using a parametric method (assuming that the groups follow a Gaussian distribution).Proceed with the following example:The manager of a supermarket chain wants to see if the ... [Read more...]

Wilcoxon signed rank test

July 29, 2009 | Todos Logos

Non-parametric statistical hypothesis test, for the comparison of the means between 2 paired samplesThe mayor of a city wants to see if pollution levels are reduced by closing the streets to the car traffic. This is measured by the rate of pollution every 60 minutes (8am 22pm: total of 15 measurements) in a ... [Read more...]

Beta Verson of tikzDevice Released!

July 28, 2009 | cameron

The tikzDevice package provides a new graphics device for R which enables direct output of graphics in a LaTeX-friendly way. The device output consists of files containing instructions for the TikZ graphics language and may be imported directly into LaTeX documents using the \input{} command. The beta version of tikzDevice ... [Read more...]

I know it’s been so long…

July 28, 2009 | the R user...

Hey,I know it's been so long since last time I posted something in here, but I was really busy with my thesis and some other stuff, but now that I have more time I promise I'll post some interesting stuff in here, by the way, I found such an ... [Read more...]

Corpus Linguistics with R, Day 2

July 28, 2009 | cornelius

R Lesson 2 text gsub ("second", "third", text) SEARCH-REPLACE-SUBJECT [1] "This is a first example sentence." [2] "And this is a third example sentence." __ gsub ("n", "X", text) [1] "This is a first example seXteXce." [2] "AXd this is a secoXd example seXteXce." __ gsub ("is", "was", text) [1] "Thwas was a first example [...] [Read more...]

Corpus Linguistics with R, Day 1

July 28, 2009 | cornelius

(This post documents the first day of a class on R that I took at ESU C&T. I is posted here purely for my own use.) R Lesson 1 __ 2+3; 2/3; 2^3 [1] 5 [1] 0.6666667 [1] 8 --- Fundamentals - Functions __ log(x=1000, base=10) [1] 3 --- (Formals describes the syntax of other [...] [Read more...]

Wilcoxon-Mann-Whitney rank sum test (or test U)

July 27, 2009 | Todos Logos

Comparison of the averages of two independent groups of samples, of which we can not assume a distribution of Gaussian type; is also known as Mann-Whitney U-test.You want to see if the mean of goals suffered by two football teams over the years is the same. Are below the ... [Read more...]

Beautiful Data

July 27, 2009 | Allan Engelhardt

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. [Read more...]

R Snippet for Sampling from a Dataframe

July 27, 2009 | Will

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 ... [Read more...]


July 27, 2009 | Stewart MacArthur

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 ... [Read more...]

Paired Student’s t-test

July 26, 2009 | Todos Logos

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...
[Read more...]

Select operations on R data frames

July 26, 2009 | Chris

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...
[Read more...]

Rosetta Code

July 26, 2009 | Paolo

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...
[Read more...]

Two sample Student’s t-test #2

July 25, 2009 | Todos Logos

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...
[Read more...]

Two sample Student’s t-test #1

July 24, 2009 | Todos Logos

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 ...
[Read more...]
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