Find the average of each row, ignore the first column

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Eric Brown 2022-4-30

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https://ww2.mathworks.cn/matlabcentral/answers/1709080-find-the-average-of-each-row-ignore-the-first-column

评论： Voss 2022-4-30

This is pretty straight foward, probaly something small I'm missing but as the title says, mean of each row starting at element 2. I'm getting a 3 by 1 array when i should be getting a 4 by 1 sized array. So whats wrong with my code?

load C.dat
A = C(:,2:end);
Cave= mean(A)';

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Riccardo Scorretti 2022-4-30

Which is the size of C?

Eric Brown 2022-4-30

C is a 2 dimensional array

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Answer 1

Voss 2022-4-30

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Let me make up a matrix C

C = (1:4)+[1;2;3;4]*10
C = 4×4
    11    12    13    14
    21    22    23    24
    31    32    33    34
    41    42    43    44

By default, mean operates along the first dimension, so this

A = C(:,2:end);
Cave= mean(A)'
Cave = 3×1
    27
    28
    29

is taking the mean of each column of A, i.e., the mean of columns 2 through 4 of C. I imagine you intended to do this

A = C(:,2:end);
Cave= mean(A')'
Cave = 4×1
    13
    23
    33
    43

But a more direct way is to specify the dimension along which mean should operate. In this case, dimension 2 to operate along the rows

Cave = mean(C(:,2:end),2)
Cave = 4×1
    13
    23
    33
    43

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Eric Brown 2022-4-30

编辑：Eric Brown 2022-4-30

I tried doing it the way you did in your last example but couldn't figure out the syntax of it so i gave up on that approach and did it the less effient way. Thank you for your help and explanation.