Matlab Array Issues

Question

I have a numerical array CentroidBins which is 3694x4. Columns 3 and 4 are arbitrary X and Y bins with a range of 1-20. My goal in the last bit of code was to go through columns 3 and 4 to count the number of times a particular pair appeared (ie. 1,1 or 1,2....etc) and place that into a 20x20 array with rows being Y bins and columns being X bins. I managed to construct something which looks like what a want, but the output is 18x17, I am assuming it is deleting rows and columns populated by "0". How can I make sure this produces 20x20?

bin20 = centroids_array / 20 %create 20 bins
imRound = round(bin20)
CentroidBins = [centroids_array , imRound]
save("CentroidBins.mat", "CentroidBins");
disp(CentroidBins)

nrow = size(CentroidBins, 1); 
B = CentroidBins(:,[3 4]); 
NumF = full(sparse(B(1:end-nrow),B(nrow+1:end),1))

how is this question different from this one? stackoverflow.com/questions/61289331/… — FangQ
– FangQ, Commented Apr 18, 2020 at 16:55
Hey @FangQ , thanks for the help on that one. It was summing the values of column 1, whereas this one is summing the number of occurrences of each pair in 3/4. Should it be approached the same way? — Ozzy
– Ozzy, Commented Apr 18, 2020 at 16:58

FangQ · Accepted Answer · 2020-04-18 17:02:41Z

2

to count the occurrence of pairs, you use hist and unique

a=[1 2; 1 2; 2 3; 8 1; 2 3];
[foo,ix,jx]=unique(a,'rows');
count=hist(jx,unique(jx)) % report the repeated counts of each unique pair
foo                       % lists the unique pairs

answered Apr 18, 2020 at 17:02

FangQ

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