'histcount​s2(y,x,Xed​ges,Yedges​)' rather than 'histcount​s2(x,y,Xed​ges,Yedges​)' gives me the correct result, why?

I have a 2-column x-y dataset, and want to obtain a density map, thus hitscounts2 is useful to count the number of point in the bin.

When I run 'histcounts2(x,y,Xedges,Yedges)', it returns a rotated 90 degree image (left image is the scatter plot):

When I run 'histcounts2(y,x,Xedges,Yedges)', it returns the good result:

What is the reason for this?

Dataset is attached.

Code is below:

load data.txt

x = data(:,1)

y = data(:,2)

n_bins = 60;

Xedges = linspace(-100,100,n_bins + 1);

Yedges = linspace(-100,100,n_bins + 1);

[N,Xedges,Yedges] = histcounts2(x,y,Xedges,Yedges);

% [N,Xedges,Yedges] = histcounts2(y,x,Xedges,Yedges);

Xbin = linspace(min(Xedges),max(Xedges), n_bins)

Ybin = linspace(min(Yedges),max(Yedges), n_bins)

[Xv,Yv] = meshgrid(Xbin, Ybin)

figure

subplot (1,2,1)

scatter (x,y,'r.')

axis equal;

subplot (1,2,2)

surf (Xv,Yv,N);

caxis([0 40]);

view (2);

axis equal;

Answer 1

[Cris LaPierre]

Because the output of histcounts2 is an array, where rows correspond to X, and columns correspond to Y. When you use surf to display an array, rows corespond to the Y axis, and columns correspond to the X axis.

Therefore, if you use surf to view the output of histcounts2, the resulting data will be flipped along the line x=y when compared to the original data inputted to histcounts2.