Bart Kastermans kasterma at kasterma.net
Thu Aug 7 17:30:36 CEST 2014

```Better:
b <- c(a[1]-1,a[-length(a)])

On 07 Aug 2014, at 17:28, Bart Kastermans <kasterma at kasterma.net> wrote:

>
>> 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 <wdunlap at 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 <wdunlap at 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 <johnnycz at 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]]
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help