How can I average a 4-D array every nth element without using too much loops
显示 更早的评论
Hi,
So I am currently working on a (476,238,1,2699) array using MatLab 2017a corresponding to (longitude, latitude, 1, time). I basically want to make a monthly average of the data (so every 5th point). The problem is I tried using a loop but it takes so much time. Here is the code I am using :
data_zeros = [];
for i = 1:2699
for j = 1:238
for k = 1:476
if (mod(i, 5) == 0)
data_zeros(k,j,1,i) = mean(data(k,j,1,i-4:i));
i
j
k
end
end
end
end
I need your insight, please help :) !
3 个评论
dpb
2018-6-21
If you have data by time for lat,long, why store in a 4D array--why not use a time table or such to make the time-based operations simpler?
What form is the time data in?
Isma Di Carlo
2018-6-22
Walter Roberson
2018-6-22
"I have a time table."
Use retime()
采纳的回答
OCDER
2018-6-21
data = rand(476, 238, 1, 2699);
N = floor(2699/5);
data_zeros = zeros(476, 238, 1, N); %Preallocate this for speed
k = 1;
for i = 5:5:2699
data_zeros(:, :, 1, k) = mean(data(:, :, 1, i-4:i), 4); %Mean along 4th dimension
k = k+1;
end
更多回答（1 个）
Walter Roberson
2018-6-21
mean( reshape(data, size(data,1), size(data,2), 5, size(data,4)/5 ), 3 )
I take advantage here of the fact that the third dimension is length 1 to pull in groups of 5 into the third dimension and mean() along that dimension.
However, you have the difficulty that your data is not an exact multiple of 5 long in that dimension. How do you want to take the mean of the entries 2696:2699 ?
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