[R] Plot Rect Transparency

[Jeff Reichman]

Duncan 

Thanks I was able to find it in the help doc.

x <- c(1,2,4,6,8,9,10,12,13,14,18,20)
y <- c(4,5,3,6,7,4,8,9,12,4,7,5)

mydata <- data.frame(x,y)

plot(mydata)
rect(5,0,8,8, col=rgb(0,1,0,alpha=0.2), border=F)

-----Original Message-----
From: Duncan Murdoch <murdoch.duncan using gmail.com> 
Sent: Thursday, June 28, 2018 7:57 PM
To: reichmanj using sbcglobal.net; R-help using r-project.org
Subject: Re: [R] Plot Rect Transparency

On 28/06/2018 5:29 PM, Jeff Reichman wrote:
> R-Help
> 
>   
> 
> Is there a way to make a rectangle transparent (alpha=0.1??)
> 
>   
> 
>    plot(c(100, 200), c(300, 450), type= "n", xlab = "", ylab = "")
> 
>     rect(110, 300, 175, 350, density = 5, border = "red")
> 
>   
> 
> Can't figure out how to take the changepoint function results and plot 
> in
> ggplot2 so I can just simply add rectangles to the plot function, but 
> I need to make transparent and there doesn't seem to be an alpha option.

Alpha is part of the colour spec.  For example,

rect(110, 300, 175, 350, density = 5, border = rgb("red")


rect(110, 300, 175, 350, density = 5, border = rgb(red=1, green=0, blue=0, alpha=0.1))

I'm not sure what is the quickest way to work out the rgb values for a named colour (col2rgb can do it, but not in a convenient format) if you want to add alpha to it.

Duncan Murdoch