3D数组的第3维的总和

Question

I have a 3 Dimensional array Val 4xmx2 dimension. (m can be variable)

Val{1} = [1, 280; 2, 281; 3, 282; 4, 283; 5, 285];
Val{2} = [2, 179; 3, 180; 4, 181; 5, 182];
Val{3} = [2, 315; 4, 322; 5, 325];
Val{4} = [1, 95; 3, 97; 4, 99; 5, 101];

I have a subscript vector:

subs = {1,3,4};

What i want to get as output is the average of column 2 in the above 2D Arrays (only 1,3 an 4) such that the 1st columns value is >=2 and <=4.

The output will be: {282, 318.5, 98}

This can probably be done by using a few loops, but just wondering if there is a more efficient way?

Answer 1

Here's a one-liner:

output = cellfun(@(x)mean(x(:,1)>=2 & x(:,1)<=4,2),Val(cat(1,subs{:})),'UniformOutput',false);

If subs is a numerical array (not a cell array) instead, ie subs=[1,3,4] , and if output doesn't have to be a cell array, but can be a numerical array instead, ie output = [282,318.5,98] , then the above simplifies to

output = cellfun(@(x)mean(x(x(:,1)>=2 & x(:,1)<=4,2)),Val(subs));

cellfun applies a function to each element of a cell array, and the indexing makes sure only the good rows are being averaged.