[R] Box plot with 5th and 95th percentiles instead of 1.5 * IQR: problems implementing an existing solution...

From: Paul Raftery <p.raftery_at_gmail.com>
Date: Sun, 17 Apr 2011 12:08:52 +0100

Hi all,

I'm just getting started with R and I would appreciate some help. I'm having trouble creating a boxplot with whiskers at the 95th and 5th percentiles instead of at 1.5 * IQR. I have read the relevant documentation, and checked existing mails on this topic. I found a small modification that should work : https://stat.ethz.ch/pipermail/r-help/2001-November/016817.html and tried to implement it.

Basically, it says to replace boxplot.stats with:

myboxplot.stats <- function (x, coef = NULL, do.conf = TRUE, do.out = TRUE)
{
nna <- !is.na(x)
n <- sum(nna)
stats <- quantile(x, c(.05,.25,.5,.75,.95), na.rm = TRUE)   iqr <- diff(stats[c(2, 4)])
out <- x < stats[1] | x > stats[5]
conf <- if (do.conf)
stats[3] + c(-1.58, 1.58) * diff(stats[c(2, 4)])/sqrt(n)   list(stats = stats, n = n, conf = conf, out = x[out & nna]) }

I entered the new function, and used fix(boxplot.default) to modify boxplot.default so that it references myboxplot.stats instead of the original boxplot.stats function.

If I now type boxplot.default, I can see that the code has been modified as expected. However, I get the exact same result as before when I create a boxplot - it shows the whiskers at 1.5 * IQR. You can test this out by creating a boxplot from the iris dataset supplied with R using boxplot(iris\$Sepal.Length ~ iris\$Species). You see that the boxplot is the same before and after the fix. Does anybody know why this occurs, and how I can get around this issue?

Thanks,

```--
Regards,
Paul

=====================
Contact Details

=====================
Paul Raftery, BEng(Hons) (Mech), Fulbright Fellow, PhD
http://www.paulraftery.com/
<http://www.paulraftery.com/>
Postdoctoral Research Engineer
Informatics Research Unit for Sustainable Engineering (IRUSE)
http://www.iruse.ie/

Department of Civil Engineering,
National University of Ireland, Galway,
Galway,
Ireland.

Landline: +353 91 49 3086
Mobile: +353 85 124 7947
Skype: praftery

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