[R] how to checking whether elements of a vector changed or not.

[Gabor Grothendieck]

Its not clear to me what your point is.  Perhaps you
could elaborate.

On Tue, Jun 2, 2009 at 4:32 PM, David Winsemius <dwinsemius at comcast.net> wrote:
> Gabor;
>
> Did you perhaps get an undesired doubling of "!"?
>
>> x1 <-c("A", "A", "B", "B", "B", "A")
>> x1[2:length(x1)] == x1[1:(length(x1)-1)]
> [1]  TRUE FALSE  TRUE  TRUE FALSE
>
>> !!diff(c(factor(x1)))
> [1] FALSE  TRUE FALSE FALSE  TRUE
>
> (Your trick of computing differences of the underlying factor representation
> ... ganz raffiniert.)
>
> --
> David Winsemius
>
> On Jun 1, 2009, at 6:21 PM, Gabor Grothendieck wrote:
>
>> Try this:
>>
>> c(FALSE, !!diff(c(factor(x))))
>>
>>
>> On Mon, Jun 1, 2009 at 11:57 AM, liujb <liujulia7 at yahoo.com> wrote:
>>>
>>> Hello,
>>>
>>> I have a vector:
>>> x <- c("A", "A", "A", "B", "A", "A", "C")
>>>
>>> I'd like to compare each of elements of vector x from its previous
>>> element
>>> (except for the 1st element which does not have previous element). So I'd
>>> like to get a vector y (of same length) that looks something like
>>> (0, 0, 0, 1, 1, 0, 1) or
>>> (F, F, F, T, T, F, T)
>>>
>>> Is there a command that do this?
>>>
>>> I was thinking to construct another variable x1 from x as follows:
>>> x1 <- vector(length=length(x))
>>> x1[1] <- x[1]
>>> x1[2:length(x)] <- x[1:(length(x)-1)]
>>> x1
>>>
>>> Now, x1 is ("A" "A" "B" "B" "B" "A"). However, I don't know how to
>>> compare 2
>>> vectors (of same length) elements by elements and a vector that indicates
>>> change or no change.
>>>
>>> Or there is a easier way to do this?
>>>
>>> Thank you very much
>>> Julia
>>>
>
> David Winsemius, MD
> Heritage Laboratories
> West Hartford, CT
>
>