Calculates the mean if the difference of two or more number is 1

Hi all;

I want to calculate mean of numbers if their difference with its neighbor is 1 . For example, if I have a matrix:

A = [9 10 12 14 15 16 18 19 22 23 25];

For each number whose difference with the neighbors is one, their mean is calculated. So, the intended result (called as matrix B):

B [9.5 12 15 18.5 22.5 25];

I try to use:

diff(A), so we get

1 2 2 1 1 2 1 3 1 2

But, how to use this diff(A) to do an operation , so that we get the resul: B [9.5 12 15 18.5 22.5 25];

Thank you for help.

Answer 1

[Matt Gaidica]

A = [9 10 12 14 15 16 18 19 22 23 25];
idx = find(diff(A)==1);
B = mean([A(idx);A(idx+1)])

I think you have a typo above, 25 would not be in the final array:

B =

    9.5000   14.5000   15.5000   18.5000   22.5000
    

Could also:

mv = movmean(A,2);
idx = find(diff(A)==1);
B = mv(idx+1)

[edward kabanyas]

Thank you very much Matt. The output that I need is like here:

B [9.5 12 15 18.5 22.5 25];

Mean is calculated for consecutive number with the diffence being 1 inclduing 14 15 16. Therefore, 14 15 16 should be only one number only, that is 15.

On the other hand, all numbers which are their difference with its neighbor is not 1, we use them as it is. Thus, the final output that I need is:

B [9.5 12 15 18.5 22.5 25];

not as your result: 9.5000 14.5000 15.5000 18.5000 22.5000

In your code, only two number is considerred.

[Matt Gaidica]

Ah. How fast does this need to be? Big arrays? A loop would be easy. Someone smarter than me might be able to work it out in a few lines.

[edward kabanyas]

Only small array actually

[edward kabanyas]

I try something like this:

Ax=diff(A);

iz=1;

while iz <= size(A,2)-1

if Ax(iz)==1 && Ax(iz+1)~=1

ikk=ikk+1;

% iz=iz+1;

finalc(ikk)=nanmean(A(iz:iz+1));

iz =iz+2;

elseif Ax(iz)==1 && Ax(iz+1)==1

ikk=ikk+1;

finalc(ikk)=nanmean(A(iz:iz+2));

iz =iz+3;

else

ikk=ikk+1;

finalc(ikk)=A(iz);

iz=iz+1;

end

I got finalc = [9.5 12 15 18.5 22.5], I lost final value (25).

with this simple I got difficulty if the array is small such as A = [9 10 12] or A = [9 10] or A = [9 12];

I need a general code that can be implemented for all size array.

[Matt Gaidica]

Not my proudest code snippet, but at least you can step through it and see what's going on:

A = [9 10 12 14 15 16 18 19 22 23 25];

B = [];
arr = [];
ii = 1;
while ii <= numel(A)
    arr(1) = A(ii);
    while ii~= numel(A) && A(ii+1) == A(ii)+1
        arr = [arr A(ii+1)];
        ii = ii + 1;
        if ii > numel(A) - 1
            break;
        end
    end
    B = [B mean(arr)];
    ii = ii + 1;
    arr = [];
end
B

[edward kabanyas]

great Matt