downsacle data by criteria of time interval

CriInterval = function(x, criteria){
  names(x) = 1:length(x)
  i=1
  while(i<length(x)){
    j=1
    while(x[i+j] - x[i] < criteria & i+j <= length(x)){
      x[i+j]<-NA
      j=j+1
    }
     i=i+j
  }
  return(names(na.omit(x)))
}

CriInterval2 = function(x, criteria){
  i=1
  j=1
  while(!is.na(i[j]) & i[j]<length(x)){
    i = c(i, match(FALSE,x[i[j]:length(x)]-x[i[j]] < criteria) + i[j]-1)
    j=j+1
  }
  return(i)
}

TS = seq(ISOdatetime(2016,02,08,18,20,00),
         ISOdatetime(2017,02,08,18,20,00), "min")
X=TS %>% sample(1e4) %>% sort %>% as.numeric()

system.time(ci <- CriInterval(X,6*60*60))
system.time(ci <- CriInterval2(X,6*60*60))
match(FALSE,X-X[1]<6*60*60) %in% ci

system.time(ci <- lapply(1:500,
       function(i) CriInterval(TS %>% sample(1e4) %>% sort %>% as.numeric(),
       criteria=6*60*60)))
str(ci)

#   user  system elapsed
#  26.25    0.05   26.29