Publications by andrew
Bags, Balls and the Hypergeometric Distribution: Update
So… the Hypergeometric distribution (as used in one of my previous posts). That was a bit of overkill, wasn’t it? To recap the problem: we have an urn filled with a selection of white and black balls. We want to calculate the probability that all of the white balls and all but one of the black balls are removed from the urn. Obviously I was j...
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Bags, Balls and the Hypergeometric Distribution
A friend came to me with a question. The original question was a little complicated, but in essence it could be explained in terms of the familiar urn problem. So, here’s the problem: you have an urn with 50 white balls and 9 black balls. The black balls are individually numbered. Balls are drawn from the urn without replacement. What is the pr...
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A Sankey Plot with Uniform Coloured Edges
Following up on my previous post about generating Sankey plots with the riverplot package. It’s also possible to generate plots which have constant coloured edges. Here’s how (using some of the data structures from the previous post too): edges$col = sample(palette, size = nrow(edges), replace = TRUE) edges$edgecol <- "col" river <- makeRive...
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Comrades Marathon Finish Predictions
* If you see a bunch of [Math Processing Error] errors, you might want to try opening the page in a different browser. I have had some trouble with MathJax and Windows Explorer. There are various approaches to predicting Comrades Marathon finishing times. Lindsey Parry, for example, suggests that you use two and a half times your recent marathon ...
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Recent Common Ancestors: Simple Model
An interesting paper (Modelling the recent common ancestry of all living humans, Nature, 431, 562–566, 2004) by Rohde, Olson and Chang concludes with the words: Further work is needed to determine the effect of this common ancestry on patterns of genetic variation in structured populations. But to the extent that ancestry is considered in gene...
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R Recipe: Reordering Columns in a Flexible Way
Suppose you have a data frame with a number of columns. > names(trading) [1] "OpenDate" "CloseDate" "Symbol" "Action" "Lots" "SL" "TP" "OpenPrice" [9] "ClosePrice" "Commission" "Swap" "Pips" "Profit" "Gain" "Duration" "Trader" [17] "System" You want to put the Trader and System colu...
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Short course on Bayesian data analysis and Stan 19-21 July in NYC!
Bob Carpenter, Daniel Lee, and I are giving a 3-day short course in two weeks. Before class everyone should install R, RStudio and RStan on their computers. If problems occur please join the stan-users group and post any questions. It’s important that all participants get Stan running and bring their laptops to the course. Class structure and...
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R sucks
I’m doing an analysis and one of the objects I’m working on is a multidimensional array called “attitude.” I took a quick look: > dim(attitude) [1] 30 7 Huh? It’s not supposed to be 30 x 7. Whassup? I search through my scripts for a “attitude” but all I find is the three-dimensional array. Where did this 2-way array come from...
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rstanarm and more!
Ben Goodrich writes: The rstanarm R package, which has been mentioned several times on stan-users, is now available in binary form on CRAN mirrors (unless you are using an old version of R and / or an old version of OSX). It is an R package that comes with a few precompiled Stan models — which are called by R wrapper functions that have the sam...
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Short course on Bayesian data analysis and Stan 18-20 July in NYC!
Jonah Gabry, Vince Dorie, and I are giving a 3-day short course in two weeks. Before class everyone should install R, RStudio and RStan on their computers. (If you already have these, please update to the latest version of R and the latest version of Stan, which is 2.10.) If problems occur please join the stan-users group and post any questions...
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