Find minimum values based on unique number

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DD_2023 2024-5-15

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评论： Mathieu NOE 2024-5-15

I have a dataset of temperatures collected over multiple depth profiles (1-147 profiles). The data is all listed in one long table, not by each profile (attached).

Each profile has a different temperature minimum, and I want to find this minimum for each profile, and colour all of the temperatures above this in grey in a figure (essentially discarding them).

Evidently I'm going about this the wrong way as my output (T_min) is all the same number (see code below).
Once I have the T_min for each profile, when I do a scatter plot, how can I colour each dot less than the T_min - for that particular profile - grey?

Thanks in advance - sorry if this isn't very clear.

j=1;
for i=1:length(dives)
    T_min(j) = nanmin(SG579_FINAL_table_MF.Cons_temp(dives));
    j=j+1;
end

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Answer 1

Mathieu NOE 2024-5-15

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https://ww2.mathworks.cn/matlabcentral/answers/2119031-find-minimum-values-based-on-unique-number#answer_1458066

在 MATLAB Online 中打开

matlab.mat

hello

the provided mat file contains 492 different profiles (and not 147)

my suggestion so far :

load('matlab.mat')

prof = Prof_temp.Profile_num;

prof_unic = unique(prof);

for k=1:length(prof_unic)

ind = (prof == prof_unic(k));

T_min(k) = min(Prof_temp.Temp(ind),[],'omitnan');

end

plot(prof_unic,T_min);

xlabel('Profile #')

ylabel('Average temperature')

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Mathieu NOE 2024-5-15

在 MATLAB Online 中打开

I have now a slight doubt when you say : one profile at a time rather than finding the depth minimum T for every profile and greying out all data shallower than that?

does "all data" mean data of each profile or all together ?

my code above was supposing greying within each profile

if it's the second option, the new code would be - hopefully again without error :

load('matlab.mat')
load('Pres.mat')
load('S.mat')
prof = Prof_temp.Profile_num;
prof_unic = unique(prof);
indgrey = [];
for k=1:length(prof_unic)
    ind = (prof == prof_unic(k));
    [T_min(k),indm] = min(Prof_temp.Temp(ind),[],'omitnan');
    Pres_of_Tmin(k) = Pres(indm);
    % indices of data to put in grey
    indgrey = [indgrey; find(Pres<Pres_of_Tmin(k))]; % find the entire data which Pres is lower than Pres_of_Tmin
                                                          % and concatenate those indexes
    
end
indgrey = unique(indgrey);
indnongrey = (1:numel(prof));
indnongrey(indgrey) = [];
scatter(S(indnongrey),Pres(indnongrey),5); % "non grey" elements
hold on 
grayColor = [.7 .7 .7];
scatter(S(indgrey),Pres(indgrey),5,grayColor); % "grey" elements
hold off
xlabel('S')
ylabel('Temp')

DD_2023 2024-5-15

Thank you! This looks more like what I was expecting. Apologies for my lack of clarity :)

Mathieu NOE 2024-5-15

ok - glad we finally converged to the solution !! :)

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Answer 2

Stephen23 2024-5-15

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在 MATLAB Online 中打开

matlab.mat

P = load('matlab.mat').Prof_temp

P = 460116x2 table

Profile_num Temp ___________ _______ 1 0.73595 1 0.73338 2 0.73372 2 0.72239 2 0.73413 2 0.7322 2 0.73786 2 0.73755 2 0.73594 2 0.74415 2 0.7336 2 0.72792 2 0.74704 2 0.75886 2 0.75926 2 0.7642

S = groupsummary(P,"Profile_num","min","Temp")

S = 492x3 table

Profile_num GroupCount min_Temp ___________ __________ __________ 1 2 0.73338 2 144 0.65173 3 2 0.73312 4 144 0.69801 5 239 0.36951 6 78 0.35654 7 79 0.70014 8 160 0.66216 9 156 0.013414 10 205 0.013662 11 442 0.00084435 12 626 0.028878 13 705 0.025135 14 959 0.015209 15 683 0.026312 16 915 -0.058026

plot(S.Profile_num,S.min_Temp)

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Stephen23 2024-5-15

编辑：Stephen23 2024-5-15

在 MATLAB Online 中打开

matlab.mat

" colour the points where the points less than the T min for that associated profile number are coloured differently."

I guess you mean where the S-values are less thatn T-min (because of course no Temp values should be less than T-min.

P = load('matlab.mat').Prof_temp

P = 460116x2 table

Profile_num Temp ___________ _______ 1 0.73595 1 0.73338 2 0.73372 2 0.72239 2 0.73413 2 0.7322 2 0.73786 2 0.73755 2 0.73594 2 0.74415 2 0.7336 2 0.72792 2 0.74704 2 0.75886 2 0.75926 2 0.7642

S = randn(size(P.Temp))

S = 460116x1

-1.9744 -0.7961 -0.0034 -0.2607 -0.4320 -1.1208 0.1508 0.5829 0.5262 -1.6224

<mw-icon class=""></mw-icon>

V = grouptransform(P.Temp,P.Profile_num,@min);

X = S<V;

scatter(S(X),P.Temp(X),23,[1,1,1]./2)

hold on

scatter(S(~X),P.Temp(~X),23)

xlabel('S')

ylabel('Temp')

DD_2023 2024-5-15

Sorry you make an excellent point and have made me realise I've completely messed up my explanation.

T_min for each profile will be located at a certain depth (called Pres, and the T_min Pres will differ between profiles). In the scatter plot of T and S, I wanted to colour any dots shallower than the T_min Pres (differing between profiles) grey.

DD_2023 2024-5-15

Here are the data for Pres and S

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Find minimum values based on unique number

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Find minimum values based on unique number

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