Filter löschen
Filter löschen

Find the first element that satisfies a condition on 3D data

6 Ansichten (letzte 30 Tage)
I'm trying to use a logical expression to find the first instance of a condition being met on a 3d matrix.
I have this dummy code for a 1d array that works the way it should:
d = randi([0 50], 100, 1);
dd = sort(d, 'descend');
pa = sum(dd);
dc = cumsum(dd);
%find row where cumsum is 50% of sum
g = find(dc >0.5*pa,1);
However, I can't get it to work on my 3d data of longitude, latitude and time (360,150,365). I want to find the n'th timestep (in the third dimension) where SC is equal to or greater than 1/2 of the sum at each latitude-longitude pair and write that to a new matrix (2d, 360X150). My current attemp is as follows:
prec = ncread(filename_p, 'Prec_gs'); % 360x150x365 matrix
p_annual(:,:) = sum(prec,3,'omitnan'); % 360x150 matrix
S = sort(prec,3,'descend'); % 360x150x365 matrix
SC = cumsum(S,3); % 360x150x365 matrix
N50(:,:) = find(SC(:,:,:) >= 0.5.*p_annual(:,:), 1);
The last row isn't working because the the dimensions are not the same (3d vs 2d), I have tried making p_annual a 3d matrix of same size as SC but still no luck.
Any thoughts on how to solve this?
  2 Kommentare
David Hill
David Hill am 24 Mai 2021
An example of your data input and expected output would be helpful.
Elin Jacobs
Elin Jacobs am 25 Mai 2021
I have attached a sample data file (20x30x365).
Code to open/read the file:
filename = 'GLDAS_cropped.nc';
ncid = netcdf.open(filename);
prec = ncread(filename, 'precipitation');
I expect to get a 20x30 matrix with the element (a number between 1 and 365) where SC is equal to or greater than 50% of p_annual. Thanks for your help.

Melden Sie sich an, um zu kommentieren.

Akzeptierte Antwort

Matt J
Matt J am 24 Mai 2021
S = sort(prec,3,'descend'); % 360x150x365 matrix
SC = cumsum(S,3,'omitnan'); % 360x150x365 matrix
p_annual = SC(:,:,end);
[~,N50] = max(SC >= 0.5.*p_annual,[], 3);
  6 Kommentare
Elin Jacobs
Elin Jacobs am 25 Mai 2021
Yep, that works, thank you so much!
Elin Jacobs
Elin Jacobs am 25 Mai 2021
To get it right, I needed to put NaN values last when sorting, but otherwise works like a charm!
S = sort(prec,3,'descend','MissingPlacement','Last');

Melden Sie sich an, um zu kommentieren.

Weitere Antworten (0)

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by