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[ferret_users] regarding top decile and bottom decile



Dear Ferreters,
G'day

I am following an example to compute the top and bottom decile of a seasonally averaged time series. The top decile means the 90th percentile and the bottom decile means 10th percentile. I want to select those years that are the top and bottom deciles of this time series to do a composite analysis. In my time series, I have 56 points as shown below.

yes? use test.nc
yes? sh da
     currently SET data sets:
    1> ./test.nc  (default)
 name     title                                                  I         J         K         L
 TS1      SSSI[D=1]/SSSI[D=1,L=@STD]       ...       ...       ...       1:56
       (T=16-SEP-1961 00:00:16-NOV-2016 00:00)
 
yes? sh gr ts1
    GRID GMH1
 name       axis              # pts                  start                end                        subset
 normal    X
 normal    Y
 normal    Z
 TMONTHLY1 TIME      56 i        16-OCT-1961 00:00    16-OCT-2016 00:00     full

I am following the sortl function to arrange my data increasing order in the time axis. Here is the script that I am writing to get top and bottom decile i.e. 90th and 10th percentile.

let npt1=`ts1,return=lend`
let srtl=sortl(ts1[l=1:`npt1`])
let arrn=samplel(ts1,srtl)
let dumy=l[g=ts1]
let mask10=if dumy eq srtl[l=`int(56*0.10)`] then 1 else 0

After this, I am not sure that the mask10 is actually representing the 10th percentile or not.

I am having a thought experiment that the bottom decile i.e. 10th percentile is the first 6 values from the srtl (arrn) variable. Because 100 percentile is represented by 56 values obtain from sortl function so represents 10th percentile is represented by 5.6 (~6 values).

So am I doing it correctly?

Let me know if I am not clear with my problem. Any help is highly appreciated.

Cheers, Saurabh


--


REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434

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