For readability I like:
> b <- c(0,a[-length(a)])
> which(a != b & a == 0)
[1] 4 12 18
> which(a != b & a == 1)
[1] 1 6 16 23
On 07 Aug 2014, at 17:23, William Dunlap <wdun...@tibco.com> wrote:
> My solution may be a bit clearer if you define the function isFirstInRun
> isFirstInRun <- function(x) {
> if (length(x) == 0) {
> logical(0)
> } else {
> c(TRUE, x[-1] != x[-length(x)])
> }
> }
>
> Then that solution is equivalent to
> which(isFirstInRun(a) & a==1)
>
> If 'a' contains NA's then you have to decide how to deal with them.
>
> (The call to 'which' is not needed if you are going to be using the
> result as a subscript.)
>
> You may also want isLastInRun
> isLastInRun <- function(x) {
> if (length(x) == 0) {
> logical(0)
> } else {
> c(x[-1] != x[-length(x)], TRUE)
> }
> }
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com
>
>
> On Thu, Aug 7, 2014 at 7:36 AM, William Dunlap <wdun...@tibco.com> wrote:
>>> a<-c(1,1,1,0,0,1,1,1,1,1,1,0,0,0,0,1,1,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1)
>>> which( a==1 & c(TRUE, a[-length(a)]!=1) )
>> [1] 1 6 16 23
>>> which( a==0 & c(TRUE, a[-length(a)]!=0) )
>> [1] 4 12 18
>>
>> Bill Dunlap
>> TIBCO Software
>> wdunlap tibco.com
>>
>>
>> On Wed, Aug 6, 2014 at 7:12 PM, Johnnycz <johnn...@yeah.net> wrote:
>>> Hello,everybody,
>>> I have a sequence,like
>>> a<-c(1,1,1,0,0,1,1,1,1,1,1,0,0,0,0,1,1,0,0,0,0,0,1,1,1,1,1,1,1,1,1,1,1),how
>>> to get the position of each first 1 and 0, that's to say, how to get
>>> b<-c(1,6,16,23) for first 1 and d<-c(4,12,18) for first 0.
>>> Many thanks!
>>> Johnny
>>> [[alternative HTML version deleted]]
>>>
>>> ______________________________________________
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>>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
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