How can I calculate the mean of certain rows of a matrix based on specific column values?

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Panos Ale
Panos Ale 2017-1-7
评论： Star Strider 2017-1-7
I have a matrix with 2 columns: example: A=[ 123 1; 444 2; 634 1; 311 1; 111 2; . . . 222 1; 312 1;]
First.I want to find the mean of the values in column 1 based on the values of column 2. Means for value 1(mean1) and for value 2(mean2).
Second. Ι want to subtract the means from the respective rows.The mean1 from the rows in column 1 that correspond to value 1 in column 2 and the mean2 from the rows in column 1 that correspond to 2 value in column 2. And take a column of the residuals without spoiling the sequence of the values.
thanks!

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Star Strider
Star Strider 2017-1-7
编辑：Star Strider 2017-1-7
This works:
A = [ 123 1; 444 2; 634 1; 311 1; 111 2; 222 1; 312 1];
Amean = accumarray(A(:,2), A(:,1), [], @mean) % Calculate Means
AmeanMtx = [Amean [1;2]] % Amean For The Appropriate Column #2 (For Demonstration Only, Can Be Deleted)
Aresd = A(:,1)-Amean(A(:,2)) % Use The Second Column To Index ‘Amean’ To Calculate The Residuals
Amean =
320.4
277.5
AmeanMtx =
320.4 1
277.5 2
Aresd =
-197.4
166.5
313.6
-9.4
-166.5
-98.4
-8.4
EDIT — Added comment documentation.

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