# [R] Boxplot in R

Adaikalavan Ramasamy ramasamy at cancer.org.uk
Mon Jul 11 03:54:28 CEST 2005

```1) The boxplot in R does the 25%, 50% and 75% mark as you want
2) Check out the range argument in boxplot. I think you can redefine
your 5% and 95% quantile in terms of IQR for symmetric distribution and
hence use this feature.

However I find it easier to calculate these numbers manually and feed it
into bxp() function. Here is one such function (with lots of room for
improvement).

matlab.boxplot <- function(m){
m  <- as.matrix(m)
bp <- boxplot(data.frame(m), plot=FALSE)

bp\$stats <- apply( m, 2, function(x)
quantile(x, c(0.05,0.25, 0.5, 0.75, 0.95), na.rm=T) )

tmp <- apply( m, 2, function(x){
under <- x[ which( x < quantile(x, 0.05, na.rm=T) ) ]
over  <- x[ which( x > quantile(x, 0.95, na.rm=T) ) ]
return( c(under, over) )
})   # always a matrix in this case
bp\$out   <- c(tmp)

bp\$group <- rep(1:ncol(tmp), each=nrow(tmp))

bxp(bp)
}

Some usage examples :

matlab.boxplot( rnorm(50) )    # a vector

my.mat <- matrix( rnorm(300), nc=3 )
matlab.boxplot( my.mat )       # a matrix

On Sun, 2005-07-10 at 18:10 -0500, Larry Xie wrote:
> I am trying to draw a plot like Matlab does:
>
> The upper extreme whisker represents 95% of the data;
> The upper hinge represents 75% of the data;
> The median represents 50% of the data;
> The lower hinge represents 25% of the data;
> The lower extreme whisker represents 5% of the data.
>
> It looks like:
>
>   ---         95%
>    |
>    |
> -------       75%
> |     |
> |-----|       50%
> |     |
> |     |
> -------       25%
>    |
>   ---         5%
>
> Anyone can give me some hints as to how to draw a boxplot like that?
> What function does it? I tried boxplot() but couldn't figure it out.
> If it's boxplot(), what arguments should I pass to the function? Thank
> you for your help. I'd appreciate it.
>
> Larry
>
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