How can I plot a graph where point colour relies on its value, based on several greater than and less than rules?

Question

Ryan Hickson 2017-4-27

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回答： Image Analyst 2017-4-27

I am trying to plot graphs where the points against the Y-axis determine the point itself to be one of five or more colours based on rules such as <0, >0 & <5, >5 & <42 etc.

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Answer 1

Image Analyst 2017-4-27

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Here's one way:

y = 10*rand(1, 150);
myColorMap = zeros(length(y), 3);
for k = 1 : length(y)
  if y(k) < 3
    myColorMap(k, :) = [1,0,0]; % Red
  elseif y(k) < 6
    myColorMap(k, :) = [1,0,1]; % Magenta
  else
    myColorMap(k, :) = [0,0,1]; % Blue
  end
end
x = 1:length(y);
scatter(x, y, 20, myColorMap, 'filled');
grid on;

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Answer 2

Steven Lord 2017-4-27

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Use your conditions to generate a vector of values that you specify as the c input in a call to the scatter function. If your conditions are simply "In the range (a, b)" (with the possibility for one or both of the endpoints to be inclusive) consider using discretize or histcounts to generate the vector.