Robin Hankin wrote:
The following caught me off-guard:
R> z <- 1i + 1:10 R> z <- Re(z) R> z [1] 1 2 3 4 5 6 7 8 9 10
as expected. But look:
R> z <- 1i + 1:10 R> make.real <- abs(z) < 1000 R> z[make.real] <- Re(z[make.real]) R> z [1] 1+0i 2+0i 3+0i 4+0i 5+0i 6+0i 7+0i 8+0i 9+0i 10+0i R>
didn't make z a real vector, which is what I wanted. ?"[<-" says
If one of these expressions appears on the left side of an assignment then that part of 'x' is set to the value of the right hand side of the assignment.
so the behaviour is as documented: class(z) is unchanged in the second session.
Would modifying "[<-" to add a test for all elements of an object being replaced (and
if this is the case to change the class of z appropriately), be a bad idea?
Sorry, but yes, a bad idea.
If you use
z[someIndex] <- someValues
you expect that z only changes its class if required to represent "someValues", but never vice versa.
That's in particular TRUE for the case of explicitly indexing all elements as in:
z <- 1i + 1:10 z[] <- 1:10
And why should R do different things in the following two cases, comparing z[1:5] <- 1:5 and z[1:10] <- 1:10 ?
Uwe Ligges
-- Robin Hankin Uncertainty Analyst Southampton Oceanography Centre European Way, Southampton SO14 3ZH, UK tel 023-8059-7743
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