Comparing numerical values of a 5x2 cell

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Pat 2020-3-31

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评论： Image Analyst 2020-3-31

Hello,

I am trying to compare all values in a 5x2 array that are below a certain threshold, and preserve the corresponding data in its particular row. For example, let's say I have a total of 5 cars but need to check which car goes a certain speed. I have a 5x2 matrix where the first column is a string and the second column are integers. I need to develop an algorithm that will return each of the cars that is below a a certain speed, say, below equal to or below 55 mph:

Red Car 50

Blue Car 45

Green Car 30

Black Car 60

Yellow Car 55

Therefore my output would need to be:

Red Car 50

Blue Car 45

Green Car 30

Yellow Car 55

I am guessing that the best way to do this will be with a few loops and an if statement to check the condition, but I am just not sure how to go about this as I am pretty new to MatLab. Any tips would be appreciated.

Thanks,

Patrick

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the cyclist 2020-3-31

编辑：the cyclist 2020-3-31

How are your car data stored? In a cell array? A table? Can you upload the data in a *.mat file, instead of just describing it?

Also, I don't understand how the 2x2 array you mention comes into play.

Pat 2020-3-31

Yes, I made a mistake. In this case it is a 5x2 cell. I am not sure how to get the cell into an array because it is a cell of cells, if that makes sense.

What I tried to do below is go through each row, looking at only the second element of the row in mph. Then I check if it is below 55. If the speed is above 55, I set that whole row to blank, thus removing it from the array. The problem is that I am getting an error that says "

Undefined function 'ge' for input arguments of type 'cell'.

for rows=1:5
       if (carData{rows,2} <= 55)
            carData{rows,2}=[]
    end 
end 

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Answer 1

Image Analyst 2020-3-31

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This will do it:

ca = {
'Red Car', 50;
'Blue Car', 45;
'Green Car', 30;
'Black Car', 60;
'Yellow Car',  55}
speeds = vertcat(ca{:, 2}) % Extract column 2.
slowSpeeds = speeds < 55 % See who is below 55
output = ca(slowSpeeds, :) % Extract only those below 55.

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Pat 2020-3-31

I think what the problem is is that right now I have my "ca" variable as a cell of cells instead of as a matrix with strings and integers.

Image Analyst 2020-3-31

Wow, how/why did it get so complicated??? Try to avoid that. Like Akira says, use a table - that's the current best approach.

Anyway, attach your actual cell array in a .mat file and I'll try to straighten it out or simplify it.

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Answer 2

Akira Agata 2020-3-31

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I would recommend storing your data as a table variable before processing, like:

% Data
ca = {
'Red Car', 50;
'Blue Car', 45;
'Green Car', 30;
'Black Car', 60;
'Yellow Car',  55};
% Arrange to table
T = table(ca(:,1),cell2mat(ca(:,2)),'VariableNames',{'CarType','Speed'});
% Extract the data where speed <= 55 mph
idx = T.Speed <= 55;
Tout = T(idx,:);

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Pat 2020-3-31

Thanks.

When I try this, it says, "Error using cell2mat (line 52)

Cannot support cell arrays containing cell arrays or objects."

I have "ca" stored as a cell of cells instead of defined as strings and numbers. The file I need to do this to has thousands of cards, so I can't set every row manually...

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