How can I store the outputs of my function into a matrix?

Hi,

I'm trying to preallocate my function so that it will return the outputs into a matrix, but it is currently only returning each output. This causes the output to be overwritten each time. I tried to set a matrix to zeroes with the desired size, but it does not fill the matrix.

For example, when inputting a simple matrix 'a',

9 1

10 3

2 6

10 10

7 10

I am getting back the following results:

d_array =

2.2361 1.0000 2.0000

d_array =

8.6023 1.0000 3.0000

d_array =

9.0554 1.0000 4.0000

d_array =

9.2195 1.0000 5.0000

d_array =

8.5440 2.0000 3.0000

d_array =

7 2 4

d_array =

7.6158 2.0000 5.0000

d_array =

8.9443 3.0000 4.0000

d_array =

6.4031 3.0000 5.0000

d_array =

3 4 5

d_array =

3 4 5

However, I want them to all appear in one matrix, stacked on top of each other in a 10 x 3. Also, I have no idea why the last value repeats itself.

Any ideas?

function d_array = d_calc(arr)
n = size(arr);
    nrows = n(1,1);
    ncol = n(1,2);
    d_array = zeros(((nrows*(nrows-1))/2), ncol+1);
    for i=1:(nrows)
        for j=i+1:(nrows)
            d = mydistance(arr(i,:), arr(j, :));
            d_array = horzcat(d, i, j)
        end
    end
end

[Eric Martz]

arr is any matrix. I am using 'a' currently:

a =

9 1

10 3

2 6

10 10

7 10

Answer 1

[KALYAN ACHARJYA]

#Edited:Initialize l=1 before for loop

d_array={};
m=1
for...
d_array{m}=horzcat(d, i, j);
m=m+1;

Save the all generated array in cell array.

[Eric Martz]

Thank you for your quick response, Kalyan.

I tried this, but it still does not work. It says "Unable to perform assignment because the left and right sides have a different number of elements."

[KALYAN ACHARJYA]

Error, in which line?

In cell array you can keep all types of data, irrespective of all sizes.

[Eric Martz]

It gives an error at line 10:

function d_array = d_calc(arr)
n = size(arr);
    nrows = n(1,1);
    ncol = n(1,2);
    d_array={};
    d_array = zeros(((nrows*(nrows-1))/2), ncol+1);
    for i=1:(nrows)
        for j=i+1:(nrows)
            d = mydistance(arr(i,:), arr(j, :));
            d_array{j} = horzcat(d, i, j)
        end
    end
end

[KALYAN ACHARJYA]

Edited Answer, Please check & let me know. Do reply first

[Eric Martz]

This still did not work. It says: Unable to perform assignment because the left and right sides have a different number of elements.

Error in d_calc (line 10)

d_array(l) = horzcat(d, i, j)

Also, I wasn't sure if you meant l = 1, l = l, or i = 1, because 'l' was kind of confusing...

function d_array = d_calc(arr)
n = size(arr);
    nrows = n(1,1);
    ncol = n(1,2);
    d_array = zeros(((nrows*(nrows-1))/2), ncol+1);
    for i=1:(nrows)
        l = 1
        for j=i+1:(nrows)
            d = mydistance(arr(i,:), arr(j, :));
            d_array(l) = horzcat(d, i, j)
            l = l + 1
        end
    end
end

[KALYAN ACHARJYA]

Please do share arr and mydistance file

[Eric Martz]

function d = mydistance(pta,ptb)
d2=(pta(1,1)-ptb(1,1))^2+(pta(1,2)-ptb(1,2))^2;

d = sqrt(d2);
end

[Eric Martz]

arr =

9 1

10 3

2 6

10 10

7 10

[KALYAN ACHARJYA]

Yes see its working

Main Script:

arr=[9,1;10,3;2,6;10,10;7,10];
d_array=d_calc(arr);

Command window:

>> d_array
d_array =
  1×4 cell array
    [1×3 double]    [1×3 double]    [1×3 double]    [1×3 double]

Here d_array as cell array, you can acess any array. If you want to access the second cell array then, in command window

    >>d_array{2} %Same for others

Function file:

function d_array = d_calc(arr)
n = size(arr);
    nrows = n(1,1);
    ncol = n(1,2);
    d_array = {};  %Changes here preallocation as cell array
    for i=1:(nrows)
        for j=i+1:(nrows)
            d = mydistance(arr(i,:), arr(j, :));
            d_array{j-1}= horzcat(d, i, j);
        end
    end
end

Good Night!

[Eric Martz]

I'm sorry for the confusion. Mine is still not working. Here is what I now have. Is this what you wrote?

function d_array = d_calc(arr)
n = size(arr);
    nrows = n(1,1);
    ncol = n(1,2);
    d_array = zeros(((nrows*(nrows-1))/2), ncol+1);
    l = 1;
    for i=1:(nrows)
        for j=i+1:(nrows)
            d = mydistance(arr(i,:), arr(j, :));
            d_array(l) = horzcat(d, i, j)
            l = l+1;
        end
    end
end

[KALYAN ACHARJYA]

Please check my last answer, I have done the little changes.You have to call the function file from Main Script.

[Eric Martz]

Okay, I tried what you did and did work but not entirely. It only returned 4 of the 10 values. It did not return the distances from point 1 to 3 for example, but only 1 to 2, 2 to 3, 3 to 4, and 4 to 5.

[KALYAN ACHARJYA]

Replace the file

function d_array = d_calc(arr)
    n=size(arr);
    nrows=n(1,1);
    ncol=n(1,2);
    d_array={};
    m=1;
    for i=1:nrows
        for j=i+1:nrows
            d=mydistance(arr(i,:), arr(j,:));
            d_array{m}=horzcat(d,i,j);
            m=m+1;
        end
    end
end

Result:

d_array =
  1×10 cell array
  Columns 1 through 7
    [1×3 double]    [1×3 double]    [1×3 double]    [1×3 double]    [1×3 double]    [1×3 double]    [1×3 double]
  Columns 8 through 10
    [1×3 double]    [1×3 double]    [1×3 double]

Rest are same, please note multiple use of loops are no recomended, see vectorization.

Good Night!

[Eric Martz]

Woohoo! Thank you so much, Kalyan!

[KALYAN ACHARJYA]

Welcome @Eric