How to plot the mean value of X corresponding to each Y value?

Question

Alejandra Uguet de Resayre 2023-1-11

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评论： Star Strider 2023-1-13

Hello!

I want to plot a vertical profile of temperature (so Y-axis is depth (m) and X-axis is temperature (ºC)). Because I have many measurements for each depth, what I get is a profile made of a cloud of points:

However, I would like to get a linear profile, so I guess I would need to plot each X mean value for each Y, right?

Could someone please help me on that?

Thanks a lot!

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Alejandra Uguet de Resayre 2023-1-11

It doesn't let me attach the mat file because it is too big (more than 5MB).

What I mean is that from that cloud of points I want to get something like this instead, like a single line thing, so I guess that's the mean value of X for each Y.

Thank you for answering!! <3 <3 <3

Star Strider 2023-1-11

@Alejandra Uguet de Resayre — Please see my latest Comment to my Answer. It produces the result matching the plot you posted.

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Answer 1

Star Strider 2023-1-11

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在 MATLAB Online 中打开

I am not certain what you want.

Perhaps something like this —

x = ones(9,1)*linspace(13, 19, 50); % Create Data

y = 8E+2*(1-exp(-5*(x-13)))-1E+3 + randn(9,size(x,2))*75; % Create Data

T = x(:); % Temperature (Assume Column Vector)

D = y(:); % Depth (Assume Column Vector)

NBins = 14; % Change This To Change Temperature Resolution

[N,Edges,Dpthv] = histcounts(D, NBins);

Ctrs = Edges(1:end-1) + mean(diff(Edges)); % Depth Centers

% Tvct = linspace(min(T), max(T), NBins);

TempMean = accumarray(Dpthv, T, [], @mean) % Calculate Mean Temperature At Each Depth

TempMean = 14×1

13.0000 13.0000 13.0000 13.0000 13.1224 13.1224 13.1224 13.1837 13.6234 15.5923

figure

plot(T, D, '.r', 'DisplayName','Data')

hold on

plot(TempMean, Ctrs, '.-b', 'DisplayName','Mean Temperature')

hold off

grid

xlabel('Temperature (°C)')

ylabel ('Depth (m)')

legend('Location','best')

The blue line plots depth as a function of the mean temperature.

.

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Star Strider 2023-1-11

编辑：Star Strider 2023-1-11

在 MATLAB Online 中打开

The only significant adjustment to my code to make it work with your data is to add 'omitnan' to the mean call in the accumarray call —

TempMean = accumarray(Dpthv, T, [], @(x)mean(x,'omitnan'))

I assigned ‘theta’ to ‘T’ and ‘dep’ to ‘D’ and increased ‘NBins’ to 50 to provide a smoother curve, and negated ‘D’ and‘Ctrs’ in their respective plot calls.

Try this —

LD = load(websave('matlab','https://www.mathworks.com/matlabcentral/answers/uploaded_files/1259980/matlab.mat'));

candec18tCopy = LD.candec18tCopy;

theta = candec18tCopy.theta;

dep = candec18tCopy.dep;

T = theta; % Temperature (Assume Column Vector)

D = dep; % Depth (Assume Column Vector)

NBins = 50; % Change This To Change Temperature Resolution

[N,Edges,Dpthv] = histcounts(D, NBins);

Ctrs = Edges(1:end-1) + mean(diff(Edges)); % Depth Centers

Tvct = linspace(min(T), max(T), NBins);

TempMean = accumarray(Dpthv, T, [], @(x)mean(x,'omitnan')) % Calculate Mean Temperature At Each Depth

TempMean = 50×1

15.9333 15.9292 15.8779 15.7944 15.5730 15.3716 14.8180 14.3202 14.0491 13.8852

figure

plot(T, -D, '.r', 'DisplayName','Data')

hold on

plot(TempMean, -Ctrs, '.-b', 'DisplayName','Mean Temperature')

hold off

grid

xlabel('Temperature (°C)')

ylabel ('Depth (m)')

legend('Location','best')

EDIT — Minor format improvements. Code unchanged.

.

Alejandra Uguet de Resayre 2023-1-13

You all are right :) Thank you both for your time invested, it helped me so much.

Star Strider 2023-1-13

As always, my pleasure!

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Answer 2

Mathieu NOE 2023-1-11

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hello

yes i'm coming late in the show... nevertheles I am here !!

just for the fun and FYI

your data could be decimated up to factor 100 without loss of quality I think

without decimation :

with decimation factor 50

code

load('matlab.mat');
temp = candec18tCopy.theta;
depth = -candec18tCopy.dep;
% remove nan's
idx = isnan(temp);
temp(idx) = [];
depth(idx) = [];
% sort 
[temp,id] = sort(temp,'ascend');
depth = depth(id);
% unique
[temp,IA,IC] = unique(temp);
depth = depth(IA);
% decimation
decim_fact = 50; % test with 1 to 100
ind = 1:decim_fact:numel(depth);
temp = temp(ind);
depth = depth(ind);
% remove data below 13.25
ind = (temp<13.25);
temp(ind) = [];
depth(ind) = [];
depth_s = smoothdata(depth,'movmedian',round(10000/decim_fact));
plot(temp,depth,'*r',temp,depth_s,'-b')