[R] find longest consecutive streak in double

[Jim Lemon]

Hi Nick,
I think you want to get the maximum run length:

jja<-runif(92,0,16)
med_jja<-median(jja)
med_jja
[1] 7.428935
# get a logical vector of values greater than the median
jja_plus_med<-jja > med_jja
# now get the length of runs
runs_jja_plus_med<-rle(jja_plus_med)
# finally find the maximum run length
max(runs_jja_plus_med$lengths)
[1] 5

Jim


On Mon, Jun 6, 2016 at 5:51 AM, Nick Tulli <nick.tulli.95 at gmail.com> wrote:
> Hey guys. Learning R after gaining a background in Python this year,
> and I'm translating my Python projects to R now. This is the first
> time I'm posting to the mailing list.
>
> Essentially, I have 92 data points in one double that I created from a
> netcdf file. Those 92 data points represent a measurement from a
> location over the course of three months. From there I've calculated
> the median value of the data, which is 8.534281. My goal here is to
> test each data point to see if it exceeds the median value, and, next,
> calculate the longest streak of days in the 92-day span in which the
> data exceeded the median value.
>
> To achieve this in Python, I've created the following function, where
> q is a vector of length 92 and q_JJA_median is, of course, the median
> value of the dataset.
> ######################################
> def consecutive(q, q_JJA_median):
>     is_consecutive = 0
>     n = 0
>     array_exceed = []
>     for i in range(len(q)):
>         if q[i] > q_JJA_median:
>             n+=1
>             is_consecutive = 1
>         else:
>             if is_consecutive:
>                 array_exceed.append(n)
>                 n = 0
>                 is_consecutive = 0
>     if q[i] > q_JJA_median:
>         array_exceed.append(n)
>     if len(array_exceed) == 0:
>         array_exceed = 0
>     if type(array_exceed) is int:
>         array_exceed = [0]
>     return array_exceed
> #######################################
>
> Here is my work thus far written for R:
> #######################################
> is_consecutive = 0
> n = 0
> array_exceed <- c()
> for (i in q) {
>   if (i > q_JJA_median) {
>     n = n + 1
>     is_consecutive = is_consecutive + 1
>   }
>   else {
>     if (is_consecutive) {
>       append(array_exceed, n)
>       n <- 0
>       is_consecutive <- 0
>     }
>   }
>   if (i > q_JJA_median) {
>     append(array_exceed,n)
>   }
> }
> #######################################
>
> My code written for R has been changed and manipulated many times, and
> none of my attempts have been successful. I'm still new to the syntax
> of the R language, so my problem very well could be a product of my
> lack of experience.
>
> Additionally, I read on a forum post that using the append function
> can be slower than many other options. Is this true? If so, how can I
> circumvent that issue?
>
> Thank you!
>
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