# Re: [R] Boxplot in R

Date: Mon 11 Jul 2005 - 11:54:28 EST

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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