Is there a faster alternative for Cell array?

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AKSHAY PUJARI 2020-4-28

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https://ww2.mathworks.cn/matlabcentral/answers/521312-is-there-a-faster-alternative-for-cell-array

回答： dpb 2020-4-28

I have the following for loop that classifies the speed and temperature values into classes and stores the value in cell arrays.

My aim is to reduce the time of calculation.Cell format appears to be relatively slow.

speed=[23   337    510   0.0104    450];
Temperature=[35 45 55 65 75];
for  t=1:size(speed,2)
        Temp_class=round( (Temperature(t)-35)/5+1 );%Temp_classs values are 1,2,3etc
        if abs(speed(t))<1
            Spd_class=1;
        elseif (1<=speed(t)) && (speed(t)<(500)
            Spd_class=2;
        else
            Spd_class=round( (speed(t)-0)/250 +2 );%Spd_class values are 1,2,3 etc
        end
        Result{Temp_class,Spd_class}=[Result{Temp_class,Spd_class};[t,Temperature(t),speed(t)]];
end

The main requirement is to identify the speed and temperature data points that belong to the same class.

For Ex: all the speed,Temperature data points with speed class 5 and temperature class 2 will be stored in cell array at {2,5}.

I would like to find a alternative faster way of storing the data.

Thanks in advance

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dpb 2020-4-28

编辑：dpb 2020-4-28

在 MATLAB Online 中打开

Result{Temp_class,Spd_class}=[Result{Temp_class,Spd_class};[t,Temperature(t),speed(t)]];

is the bottleneck, you're dynamically reallocating the cell content every pass.

There's also an unbalanced parenthesis on elseif (1<speed(t)) && (speed(t)<(500)

elseif (1<speed(t)) && (speed(t)<500)

You can't return a Spd_class value of 3 -- <500 --> 2 by the second clause but

round(500/250+2) ==> 4, not 3 to be continuous

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Answer 1

dpb 2020-4-28

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/521312-is-there-a-faster-alternative-for-cell-array#answer_428918

在 MATLAB Online 中打开

Just store the class data with the position/time variable in 2D array. Use grouping variables to process by class either singly or jointly.

if abs(speed)<1
  sclass=1;
elseif speed>=1 & speed<500
  sclass=2;
else 
  sclass=fix(speed/250)+1;
end
tclass=fix((Temperature-35)/)5+1;
TSclasses=[1:numel(speed);sclass;tclass].';