MATLAB: How to connect the dots in the plot

newplotplotting

Basically if I plot it 'x' it looks fine but if I plot '–' the lines connect in crazy pattern. What can I do?
Its really annoying me. I know that I can sort the data to match up with the correct points but to be honest I'm not sure how to do that.
please find attached source files and data,

Best Answer

Another approach:
D = load('Dustin Braun PL0Data (6).mat');
x = D.x;
y = D.y;
A = [x.^3 ones(size(x))];
p = A\y;
x1 = linspace(min(x), max(x))';
y1 = [x1.^3  ones(size(x1))]*p;
figure(1)
plot(x, y, 'o', x1, y1, '-r')
grid
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