Simpler code for aggregating data by sum

Hello,

given matrix A: A=[4 0.5;4 0.25;1 0.125; 2 0.2;4 0.6;3 0.2; 1 2/3; 2 1; 2 1/16;4 0.5]

asked: Aggregate data in first column by sum

desired result:

1.0000 0.7917

2.0000 1.2625

3.0000 0.2000

4.0000 1.8500

I composed a code, but it work half, it can not make the data unique. So it fails at : G=unique(List)

Can somebody tell me why it fails at that point? And is there a more straight forward code for this whole proces? Maybe inbuilt functions? Can I get some feedback pls?

This is my code:

List=[];

% Make list unique

for i=1:size(A,1)

F=A(A(:,1)==A(i,1),:); %subsetting all rows

ElementList=[A(i,1) sum(F(:,2))]; %adding the sum of the subset to a row

List=[List; ElementList] % saving row plus its aggregated sum to a list

end

G=unique(List) %making the list unique

kind regards,

[rakbar]

Try this:

G = findgroups(A(:,1));
A=[4 0.5;4 0.25;1 0.125; 2 0.2;4 0.6;3 0.2; 1 2/3; 2 1; 2 1/16;4 0.5] 
func = @(x)sum(x);
Y = splitapply(func,A(:,2),G);
[unique(G) Y]

ans =

    1.0000    0.7917
    2.0000    1.2625
    3.0000    0.2000
    4.0000    1.8500

[Akira Agata]

Or simply:

A = [4 0.5;4 0.25;1 0.125; 2 0.2;4 0.6;3 0.2; 1 2/3; 2 1; 2 1/16;4 0.5];
B = splitapply(@sum,A(:,2),A(:,1));

The result is:

>>[unique(A(:,1)), B]

ans =

1.0000 0.7917

2.0000 1.2625

3.0000 0.2000

4.0000 1.8500

[Clarisha Nijman]

Thank you dear friends!!! Suggestion woks perfect!

Answer 1

[OCDER]

A=[4 0.5;4 0.25;1 0.125; 2 0.2;4 0.6;3 0.2; 1 2/3; 2 1; 2 1/16;4 0.5]
Results = [unique(A(:, 1)), accumarray(A(:, 1), A(:, 2))];

Results =

    1.0000    0.7917
    2.0000    1.2625
    3.0000    0.2000
    4.0000    1.8500

[Clarisha Nijman]

Thank you dear friends!!! Suggestion woks perfect!

[Clarisha Nijman]

Dear all,

I want to apply your instructions in my case, but do not fully understand how to use these instructions. It regards aggregating rows based of three columns by sum of the forth column.

% a simplified version of my case looks like:

A=[2.0000 3.0000 4.0000 0.01;

2.0000 3.0000 4.0000 0.05;

3.0000 2.0000 4.0000 0.01;

3.0000 4.0000 2.0000 0.02;

1.0000 2.0000 3.0000 0.03;

2.0000 3.0000 4.0000 0.00;

1.0000 2.0000 3.0000 0.02;

2.0000 3.0000 4.0000 0.01;

2.0000 3.0000 4.0000 0.01;

3.0000 2.0000 4.0000 0.07];

% Aggregated the first three columns by sum of the 4th column

% The result should be:

E= [1.0000 2.0000 3.0000 0.05;

2.0000 3.0000 4.0000 0.08;

3.0000 2.0000 4.0000 0.10];

This is how I tried to adapt your suggestions. But I am getting errors.

% % Code 1:

G = findgroups(A(:,1:3));

func = @(x)sum(x);

Y = splitapply(func,A(:,4),G);

E=[unique(G) Y];

% Code 2:

B = splitapply(@sum,A(:,4),A(:,1:3));

E=[unique(A(:,1:3)), B]

% Code 3:

E = [unique(A(:, 1:3)), accumarray(A(:, 1:3), A(:, 4))];

Can I have your feedback?

[OCDER]

Check your results, as you have [3 4 2] unique combo.

 A=[2.0000    3.0000    4.0000    0.01;
    2.0000    3.0000    4.0000    0.05;
    3.0000    2.0000    4.0000    0.01;
    3.0000    4.0000    2.0000    0.02;
    1.0000    2.0000    3.0000    0.03;
    2.0000    3.0000    4.0000    0.00;
    1.0000    2.0000    3.0000    0.02;
    2.0000    3.0000    4.0000    0.01;
    2.0000    3.0000    4.0000    0.01;
    3.0000    2.0000    4.0000    0.07];

[UnqVal, ~, UnqGrpNum] = unique(A(:, 1:3), 'rows');
E = [UnqVal, accumarray(UnqGrpNum, A(:, end))];
E =
    1.0000    2.0000    3.0000    0.0500
    2.0000    3.0000    4.0000    0.0800
    3.0000    2.0000    4.0000    0.0800
    3.0000    4.0000    2.0000    0.0200

[Clarisha Nijman]

Ok I see, you have to assign the unique groups a number, such that you can refer to them in the accumarray function. If would never come up with such a good idea. I worked with for loops and the code runs very very long. I indeed missed the unique combo[3 4 2] in my results.

Thanks a lot!!!