How can I compute histogram using three variable

I have three variable, for e.g latitude, longitude and temperature. For each latitude and longitude, I have corresponding temperature value. I want to plot latitude v/s longitude plot in 5 degree x 5 degree grid , with mean temperature value inserted in that particular grid instead of occurring frequency.

Answer 1

[Akira Agata]

The strait-forward way to do this will be like this (well, there should be more sophisticated way...). I hope it will be help you somehow!

% Sample data
[latGrid,lonGrid] = meshgrid(25:45,125:145);
T = table(latGrid(:),lonGrid(:),randi([0,35],size(latGrid(:))),...
  'VariableNames',{'lat','lon','temp'});

% Discretize with 5 degree
[latGroupID, latEdge] = discretize(T.lat, 25:5:45);
[lonGroupID, lonEdge] = discretize(T.lon, 125:5:145);

% Add 5 degree mesh ID to the table T
[C,~,ic] = unique([latGroupID,lonGroupID],'rows');
T.meshID = ic;

% Calculate mean temperature in 5 degree mesh
Output = table(latEdge(C(:,1))',lonEdge(C(:,2))',...
  splitapply(@mean,T.temp,T.meshID),...
  'VariableNames',{'latEdge','lonEdge','aveTemp'});

% Visualize the output
heatmap(Output,'latEdge','lonEdge','ColorVariable','aveTemp');

[Aristo]

Hello, thank you so much for the solution, but I am getting error stating "Error using discretize, Too many output arguments."

[Akira Agata]

Maybe your MATLAB is not the latest one. In MATLAB R2015x and R2016a, discretize supports only one output argument. After R2016b, it supports two output arguments. So, please check your MATLAB version.

[Akira Agata]

Hi Aristo-san, by slightly changing the last part of my code to the following, similar heatmap figure can be generated.

h = heatmap(Output,'latEdge','lonEdge','ColorVariable','aveTemp');
h.GridVisible = 'off';
h.CellLabelColor = 'none';
h.Colormap = jet;