[R] explanation for left-side behaviour

[Antje]

Hi there,

I'm pretty sure that it's written down somewhere but I cannot find it so 
far.

The little example shows different approaches to replace a substring. 
Only the last one works. I think it has something to do with the fact 
that "substr" is used on the left side. Can anybody refer to an 
explanation for this behaviour?

Thanks a lot in advance!

Antje



values <- factor(c(rep("abc",3), rep("bcd",3), rep("cde",3)))

substr(values,2,3) <- ".."
substr(as.character(values),2,3) <- ".."

values <- as.character(values)
substr(values,2,3) <- ".."