MATLAB: How to group rows based on unique value in the first column

group data

I have several excel worksheets with over 6000 rows of data in excel that go across multiple columns. In column 1 I have the number corresponding to an image (goes up sequentially) and in column 2 I have the cell number that goes up sequentially to a maximum number which varies image to image. I need to extract the maximum number of cells per image but I'm not sure how to script it in matlab.
Matrix Example to illustrate problem:
1       1
1       2
1       3
2       1
3       1
3       2
3       4
3       5
etc.
and I need an output that resembles
1      3
2      1
3      5
etc.

Best Answer

A = [1 1
     1 2
     1 3
     2 1
     3 1
     3 2
     3 4
     3 5];
A1 = unique(A(:,1));
A2 = accumarray(A(:,1),A(:,2),[],@max)
output = [A1 A2]
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