Monthly Archives: June 2012

Grouped means (or anything else…)

June 25, 2012
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Grouped means (or anything else…)

An easy one today, but something that stumped me for a while* the first time I tried it out. How do you get a group mean (or other summary statistic) from R? Lets say you have a Y variable that represents repetitions for each of however many factors. You could subset the data by each

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Example 9.36: Levene’s test for equal variances

June 25, 2012
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Example 9.36: Levene’s test for equal variances

The assumption of equal variances among the groups in analysis of variance is an expression of the assumption of homoscedasticity for linear models more generally. For ANOVA, this assumption can be tested via Levene's test. The test is a function of the residuals and means within each group, though various modifications are used, including the Brown-Forsythe...

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Euro 2012: Day 18

June 25, 2012
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Euro 2012: Day 18

As promised. Looks like a Spain Germany final.

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How many ecologists were on ECOLOG in 1992?

June 25, 2012
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How many ecologists were on ECOLOG in 1992?

Remember 1992? I had just turned 13 and was still a year away from highschool when my true descent into nerdom and the internet would begin. Back then it was with a local BBS (Bulletin Board System) run by a guy in a trailer park named Charlie and a 1200 baud modem on...

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Making Reproducible Research Enjoyable

June 25, 2012
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Making Reproducible Research Enjoyable

Note: this is a contributed article for the ICSA Bulletin and the basic idea can be summarized in this picture. It is hard to convince people to think about reproducible research (RR). There are two parts of difficulties: (1) tools used to be for ex...

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Grid2Polygons

June 25, 2012
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Grid2Polygons

I’d like to introduce you to the Grid2Polygons function; an R function for converting sp spatial objects from class SpatialGridDataFrame to SpatialPolygonsDataFrame. The significance of this conversion is that spatial polygons can be transformed to a different projection or datum with the spTransform function in package rgdal. Postscript files created with spatial polygons are reduced in size and...

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Hodgkin-Huxley model in R

June 24, 2012
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Hodgkin-Huxley model in R

One of the great research papers of the 20th century celebrates its 60th anniversary in a few weeks time: A quantitative description of membrane current and its application to conduction and excitation in nerve by Alan Hodgkin and Andrew Huxley. Only a...

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Split-plot 1: How does a linear mixed model look like?

June 24, 2012
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Split-plot 1: How does a linear mixed model look like?

I like statistics and I struggle with statistics. Often times I get frustrated when I don’t understand and I really struggled to make sense of Krushke’s Bayesian analysis of a split-plot, particularly because ‘it didn’t look like’ a split-plot to … Continue reading →

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useR 2012: main conference braindump

June 24, 2012
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useR 2012: main conference braindump

I knew R was versatile, but DANG, people do a lot with it: > > … I don’t think anyone actually believes that R is designed to make *everyone* happy. For me, R does about 99% of the things I … Continue reading →

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reading shape files in R

June 24, 2012
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reading shape files in R

If I would like to adjust a shape file I normally used the way over an excel file or a text file to get a table and to join this with an existing shape file. Due to the sp and rgdal packages in R you can manipulate shapefiles directly in R: now lets map the

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