How to find the indices of same values within a vector and bin them together

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MatlabUser17
MatlabUser17 2018-4-24
评论： Star Strider 2018-4-25
I have two vectors with the same length (N). For example:
A=[ 1 2 3 3 3 3 4 5]; B=[ 9 8 7 6 5 6 7 8];
What I need to do is to take an average over elements in vector 'B' that their corresponding indices in vector 'A' have same values. In this example, element 3,4,5,6 in vector A are all equal to '3' so I need to take an average over (7+6+5+6/4) in vector B. I need to do this over a large data and bin them together. I tried different ways and it didn't work. How can I do this?
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MatlabUser17
MatlabUser17 2018-4-24
I want to keep the other elements as well. Obviously, since the other elements have not been repeated in this example the average over one element is the same, but if they repeat I will take an average of them as well.
In summary, I need to find the same values from vector A and bin them together and take an average over their corresponding values in vector B.
let's say I have a large data:
kk=find(~isnan(B)); A=A(kk); B=B(kk); [A,IX]=sort(A); B=B(IX); u=unique(A) hist1=histc(A,u)
Up to here I have sorted the data from small to large, and have found similar values in A with their number of repetition. But I need to find their indices so I can extract them from B and take the average.

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采纳的回答

Ameer Hamza
Ameer Hamza 2018-4-24
The following statement will return the list of all the averages according to the way you mentioned in your question.
meanVector = splitapply(@(x) mean(x), B', A')
since A have 5 unique elements, meanVector will also contain 5 elements corresponding to the mean value from B.
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Star Strider
Star Strider 2018-4-25
编辑：Star Strider 2018-4-25
See if this works with your data:
A=[ 1 2 3 3 3 3 4 5];
B=[ 9 8 7 6 5 6 7 8];
[Au,~,ix] = unique(A(:),'stable'); % Unique Elements & Indices (Convert To Column Vector), Keep Original Order
Ar_mean = accumarray(ix, B, [], @mean); % Means Of Single & Repeated Values
Result = [Au, Ar_mean] % Elements Of ‘A’ In Column #1, Corresponding ‘mean’ Of ‘B’ In Column #2
AB_Tbl = table(Au, Ar_mean) % Table (Optional)
Result =
1 9
2 8
3 6
4 7
5 8
AB_Tbl =
Au Ar_mean
__ _______
1 9
2 8
3 6
4 7
5 8
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MatlabUser17
MatlabUser17 2018-4-25
编辑：MatlabUser17 2018-4-25
Thanks, Star! it works, I got similar results from both answers. I wanted to accept both answers but seems like it's not possible. I really appreciate your help.

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