On Tue, Apr 7, 2009 at 8:13 AM, Melissa2k9 <m.mcquillan@lancaster.ac.uk>wrote:

>
> I am trying to make a sequence and am  using a for loop for this. I want to
> start off with an initial value ie S[0]=0 then use the loop to create other
> values. This is what I have so far but I just keep getting error messages.
>

R only allows positive integer subscripts, and defines s[0] as the empty
vector.

You might think that assigning to an empty vector would give an error, but R
semantics say instead that this is a no-op. This is so that things like s[
<<some boolean condition>> ] <- value will assign the value to all elements
of s meeting the condition -- while allowing for the possibility that none
of them meet that condition.

If you try to assign to an illegal individual element, however, you do get
an error:

     s[[0]] <- 45       # gives an error

R's subscripting semantics are very convenient for many operations, but do
take some getting used to.

            -s

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