Sorting large vector onto 2D grid
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Hi all,
I would like to sort a vector of measurements onto a 2D grid, by the corresponding latitude and longitude.
I start with a vector of measurements (meas), a vector which lists which row the value corresponds to (row), and a vector which lists which column the value corresponds to (col). 'row' and 'col' are calculated from the latitude and longitude of the raw file data.
If I am using a (360,720) grid, I could do the following:
for i = 1:360
for j = 1:720
index = find(row== i & col == j);
values = meas(index) *NB
end
end
*NB I realise this line would give an error - it is simplified slightly for the sake of this post. Essentially what I do in my actual code here is store the values as a 3D grid (row, col, #measurements).
This is really quite slow. I have been playing with alternatives, but can't quite get my head around how to do this faster. I have been sorting by 'row' and 'col' as in the accepted answer to this question....
This got me close, but I couldn't quite adapt this method for use with two sorts (row and col).
Anyone got any ideas as to how to do this, without using find in a loop. With (360 x 720) grid cells, that's a lot of calls to 'find'!
Thanks,
Dom
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Accepted Answer
Thorsten
on 24 Jan 2013
sz = [360 720];
ind_list = sub2ind(sz, row, col);
for i = 1:360
for j = 1:720
index = 360*(j - 1) + i;
values{i, j} = meas(find(ind_list == index));
end
end
More Answers (1)
Thorsten
on 24 Jan 2013
sz = [360 720];
ind = sub2ind(sz, row, col);
values = zeros(sz);
values(ind) = meas;
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