CODEWITHSUNDEEP
arraysmatlabmean
ryh12
ryh12

Reputation: 367

Average of each two columns in an array

I have an array as follows:

arr=[2 3 4 5 6 7 8 9 1 2 3 4];

How can I get the average of each two columns, so that the result is:

ans=[2.5 4.5 6.5 8.5 ...];

Upvotes: 0

Views: 105

Answers (2)

TroyHaskin
TroyHaskin

Reputation: 8401

Convert it into a two-row matrix using reshape, sum, and divide-by-2:

>> arr=[2 3 4 5 6 7 8 9 1 2 3 4];
>> arrbar = sum(reshape(arr,2,[]))/2

arrbar =

    2.5000    4.5000    6.5000    8.5000    1.5000    3.5000

Augmenting the solution per your comments to this answer, we can guard against odd lengths with a little indexing trick:

>> arrbar = sum(reshape([arr,arr(end:end-(mod(end,2)==0))],2,[]))/2
arrbar =
    2.5000    4.5000    6.5000    8.5000    1.5000    3.5000

>> arr=[2 3 4 5 6 7 8 9 1 2 3 4 6];
>> arrbar = sum(reshape([arr,arr(end:end-(mod(end,2)==0))],2,[]))/2
arrbar =
    2.5000    4.5000    6.5000    8.5000    1.5000    3.5000    6.0000

The extra indexing appends the final element for odd lengths so the final average is simply the final element.

Upvotes: 3

KKS
KKS

Reputation: 1389

How about using convolution?

arr=[2 3 4 5 6 7 8 9 1 2 3 4];

arr2=[1 1];

A=conv(arr,arr2)/2;

mean2=A(2:2:end-1)

plot(mean2)

If your array number is not always even, and you want to add final element at the end of the result array when array number is odd, 

arr=[2 3 4 5 6 7 8 9 1 2 3 4 6];

arr2=[1 1];

A=conv(arr,arr2)/2;

if mod(length(arr),2) == 1;

   mean2=[A(2:2:end-1) arr(end)]

else 
   mean2=[A(2:2:end-1)]
end

plot(mean2)

Upvotes: 0

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