Finding the averages for a unique value.

I have a data set as shown, I need to find the average values of 1 in column A w.r.t to column B, C, etc.

For example average of 1 = average of 0.7, 0.9, 1.1, 1.3, similarly

2 = average of 1.5, 1.7, 1.9

similarly for 3 , 4, ..... and on and similarly for the columns C, D, E, F.

I have written a code as detailed below but I am getting index exceeds matrix error.

clc

clear all

load input.txt

d=input(:,1);

Tm=input(:,2);

Atmp=input(:,3);

Mxtmp=input(:,4);

Mntmp=input(:,5);

Rh=input(:,6);

[u i j] = unique(d);

D = length(d) % No. of data vectors

U = length(u) % No. of unique dates

I = length(i)

J = length(j)

M = zeros(I,5); % Initialize daily means

for k=1:J

    n=find(u==d(k));

    M(j,:)= mean(input(u(d),2:6))

end

Can any one help.

Thanks in advance.

Answer 1

[Thorsten]

X = input;
A = X(:,1);
MC = arrayfun(@(i) mean(X(A == i, 2:end)), unique(A), 'UniformOutput', false);
M = reshape(cell2mat(MC), size(X,2)-1, [])'

Answer 2

[Stephen23]

This is exactly what the function accumarray is designed for! Use it either in a loop:

X = [1,   1,   1,   1,   2,   2,   2,   3,   3,   3,   4,   4,   5,   5,   5;...
   0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2.1, 2.3, 2.5, 2.7, 2.9, 3.1, 3.3, 3.5;...
  0.78,0.16,0.86,0.68,0.72,0.76,0.80,0.84,0.88,0.92,0.96,1.00,1.04,1.08,0.12].'
%
for k = size(X,2):-1:1
    out(:,k) = accumarray(X(:,1),X(:,k),[],@mean);
end

Or all on one line using cellfun:

mat = cell2mat(cellfun(@(V)accumarray(X(:,1),V,[],@mean),num2cell(X,1),'UniformOutput',false))

Both create the same numeric output:

mat =
 1    1.00000   0.62000
 2    1.70000   0.76000
 3    2.30000   0.88000
 4    2.80000   0.98000
 5    3.30000   0.74667

[Mohana]

I want to load the input file from graphic interface which is working fine and then find the result, since there are several files that need to be processed. This is only a sample data file.

[Stephen23]

So try it! As long as your data file has the same format as your example data (first column natural number group index), then this method will work.

[Mohana]

I am getting the following error for the line

out = cell2mat(cellfun(@(V)accumarray(X(:,1),V,[],@mean),num2cell(X(:,2:end),1),'UniformOutput',false

Expression or statement is incorrect--possibly unbalanced (, {, or [.

It is not clear whether the line is a single line command or a combination of multiple line.

[Stephen23]

You did not copy the final two closing parentheses '))' at the end of the functions. I just copied the complete line and it worked without error.

I wrote in my answer "...on one line...", so how is this not clear that this code should be on one single line?

Answer 3

[Andrei Bobrov]

a - your array

[ii,jj] = ndgrid(a(:,1),1:5);
out = [unique(a(:,1)), accumarray([ii(:),jj(:)],reshape(a(:,2:end),[],1),[],@mean)];