could anyone help me how to update the array values with respect to the following arrays

A= [1.0119    1.6739;
    2.8012    1.6381;
    0.0752    0.1222;
    1.3143    0.8189;
    0.7956    0.8750;
    1.8512    1.1499]
 B =[0.9512    0.4314;
    0.2490    0.8309;
    0.3864    0.8246]
C= [ 3;
     1;
     2;
     1;
     2;
     1]

I am having the above three matrices,I want to update B by considering the average values of A with respect to C.

For example,

In C i have 2nd,4th and 6th rows to be 1 which means i need to add the mentioned rows in A and find the average of it and it needs to be updated in first row of B.

in the same way,i need to add 3rd and 5th rows in A and it needs to get updated in second rows of B.

On doing this the updated B should be [1.9889 1.2023;

0.4354 0.4986;

0.3864 0.8246]

could anyone please help me on this.

Answer 1

[Alaster Meehan]

B(1,:) = mean(A(C == 1,:));

B(2,:) = mean(A(C == 2,:));

B(3,:) = mean(A(C == 3,:));

Or you can put it in a for loop.

for ii = 1:3

B(ii,:) = mean(A(C == ii,:));

end

Cheers Alaster

[jaah navi]

I tried your code with respect to the following matrix

A= [1.0119    1.6739
    2.8012    1.6381
   -0.0752    0.1222
    1.3143   -0.8189
   -0.7956    0.8750
    1.8512    1.1499]
 B =[0.9512    0.4314
    0.2490    0.8309
    0.3864    0.8246]
C =[ 3;
     1;
     2;
     1;
     2;
     1];
for ii = 1:3
    B(ii,:) = mean(A(C == ii,:))
end

when i run the code i am getting the following result

B =[1.9889    0.6564
   -0.4354    0.4986
    1.3429    1.3429]

where the last row gets changed but it should have the same values as 0.3864 0.8246.

could you please help me on this.

[Alaster Meehan]

Sorry should have specified dimension for mean().

Also add in the max value for C, to generalise the loop.

If thre is an index not present in C then this will result in a row of NaNs.

for ii = 1:max(C)

B(ii,:) = mean(A(C == ii,:),1)

end

[Andrei Bobrov]

See my answer.

Answer 2

[Andrei Bobrov]

a = (1:max(C))';
b = accumarray(C,1);
i = a(accumarray(C,1) > 1);
[lo,ii] = ismember(C,i);
AA = A(lo,:);
[iii,j] = ndgrid(ii(lo),1:size(B,2));
B(i,:) = accumarray([iii(:),j(:)],AA(:),[],@mean);

[jaah navi]

I tired with the following code

A= [1.0119    1.6739
    2.8012    1.6381
   -0.0752    0.1222
    1.3143   -0.8189
   -0.7956    0.8750
    1.8512    1.1499]
 B =[0.9512    0.4314
    0.2490    0.8309
    0.3864    0.8246]

C =[ 3;
     1;
     2;
     1;
     2;
     1];
 [i,j] = ndgrid(C,1:size(A,2));
B = accumarray([i(:),j(:)],A(:),[],@mean)

when i run the code I couldnt able to get the result which i required.

I need to have the updated B should be B =[1.9889 0.6564;

-0.4354 0.4986;

0.3864 0.8246],the last row should be as existing B as 3 is present in only once in C.

Could you please help me on this.

[Andrei Bobrov]

I'm fix.

[jaah navi]

I tried your code with respect to the following matrices

A=[1.0119    1.6739
      2.8012    1.6381
      0.0752    0.1222
      1.3143    0.8189
      0.7956    0.8750
      1.8512    1.1499];
B=[0.3788    0.6150;
    0.7567    0.4021;
    0.5070    0.1980]
C =[1;
     2;
     3;
     2;
     2;
     2]
 a = unique(C)
b=accumarray(C,1)
i = a(accumarray(C,1) > 1)
lo = ismember(C,i)
AA = A(lo,:)
[ii,j] = ndgrid(C(lo),1:size(B,2))
B(i,:) = accumarray([ii(:),j(:)],AA(:),[],@mean)

When i run the code i am getting error stating Subscripted assignment dimension mismatch.

Error in line

B(i,:) = accumarray([ii(:),j(:)],AA(:),[],@mean)

Could you please help me on this.

[Andrei Bobrov]

I'm fix.