MATLAB: How to calculate the median of a column depending on the value of another column

Question

INTRODUCTION: I have two columns of values. The values of the first column are partially constant and the values of the second column are arbitrary ones.

GOAL: I want to build a third column with values of median for each group of constant value of the first column.

EXAMPLE:

A=[1  3;
1  2;
1  3;
2  4;
2  4;
2  3;
2     4;  
3  5;
3  1;
3  1;
3  1;
3  2;
4  3;
4  2];
B1=median(A(1:3,2));
B2=median(A(4:7, 2));
B3=median(A(8:12, 2));
B4=median(A(13:14, 2));
B=[B1 B2 B3 B4]';

PROBLEM: The number m of rows are typically much larger than only 14 and makes impossible to write the commands B1 until BN per hand.

I wonder if someone could tell me how to write some command lines that makes this automatically.

Thank you in advance for your help

Emerson

Answer 1

B = accumarray(A(:,1),A(:,2),[],@median);
out = [A, B(A(:,1))];