# Mean of certain elements within a matrix

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Malik Khan am 11 Dez. 2019
Kommentiert: RAMPUNIT KUMAR am 1 Sep. 2021
I have a matrix which is a 372x6. Rather than find a mean for a specific row or a specific column, I want to find the mean of elements that lay in different rows as
Although the elements are from different rows, I have a pattern for the order in which they are to be taken. The last 2 elements (column 5 and 6) is to be averaged with the second third and fourth of the following row. The mean then needs to be found for each line. To make this easier to visualise I have written out a matrix for which we need to find 2 means. We need one mean to be of (e f h i j) and the other (k l m n o). For my case however I need to do this 371 times as we have 372 lines (obviously we can’t find mean for the first row).
(a b c d e f)
(g h i j k l)
(l m n o p q)
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RAMPUNIT KUMAR am 1 Sep. 2021
I too have a doubt, like for matrix
(a b c d e f g h I j k l m n o p q r)
I need to find the mean of a,b then c,d then e,f then g,h and so on upto last element. How could we do that if size is big enough.

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### Akzeptierte Antwort

Stijn Haenen am 11 Dez. 2019
I think this will work:
for i=1:371
Mean_i(i)=mean([matrix(i,5:6),matrix(i+1,2:4)]);
end
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### Weitere Antworten (2)

Bandar am 11 Dez. 2019
Bearbeitet: Bandar am 11 Dez. 2019
A=[1 2 3 4 5 6; 7 8 9 10 11 12;13 14 15 16 16 18;19 20 21 22 23 24]
[row,~]=size(A);
for i=1:row-1
c = A(i,[5 6]);
r = A(i+1,[2 3 4]);
B = [c r]
mean(B)
end
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RAMPUNIT KUMAR am 1 Sep. 2021
RAMPUNIT KUMAR less than a minute ago ⋮ I too have a doubt, like for matrix (a b c d e f g h I j k l m n o p q r) I need to find the mean of a,b then c,d then e,f then g,h and so on upto last element. How could we do that if size is big enough.

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Andrei Bobrov am 11 Dez. 2019
Bearbeitet: Andrei Bobrov am 11 Dez. 2019
Here A - your array (m x 6)
[m,n] = size(A);
i = repmat((0:m-1)',1,n-1);
i(:,end-1:end) = circshift(i(:,end-1:end),-1);
i = [zeros(m,1),i];
lo = i ~= 0;
out = accumarray(i(lo),A(lo),[],@mean);
or
[m,n] = size(A);
i = [zeros(m,1),reshape(circshift(repelem(0:m-1,n-1),-2),n-1,[])'];
out = accumarray(i(i>0),A(i>0),[],@mean);
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RAMPUNIT KUMAR am 1 Sep. 2021
RAMPUNIT KUMAR less than a minute ago ⋮ I too have a doubt, like for matrix (a b c d e f g h I j k l m n o p q r) I need to find the mean of a,b then c,d then e,f then g,h and so on upto last element. How could we do that if size is big enough.

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