How do I create a string for values

Question

Sebastiano Inturrisi 2018-9-6

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评论： Sebastiano Inturrisi 2018-9-6

I have written this code to produce values from 1 - 3 with set probabilities:

B = randi(3,1);
P = B;
for i = 1:50
z=rand;
if B == 1
   if z < .4
       B = 3;
   end
elseif z > .4 && z <.6
    B = 2;
elseif B == 2
    if z < .2
        B = 1;
    end
elseif z > .2 && z < .4
    B =3;
elseif B == 3
    if z < .2
        B = 1;
    elseif z > .2 && z < .25
        B = 2;
    end
end
P = [P;B];
end

I would like to give each number a name, so 1 = A, 2 = B and 3 = C. I tried doing this:

for c = 1:50
    if P(c) == 1
        P(c) = "A";
    elseif P(c) == 2
        P(c) = "U";
    else
        P(c) = "D";
    end
end

but I keep receiving NaN. What am I doing wrong?

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YT 2018-9-6

Please format your code using the "{}code" button

Sebastiano Inturrisi 2018-9-6

Just fixed this issue, sorry about that.

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Answer 1

jonas 2018-9-6

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编辑：jonas 2018-9-6

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The class of P is double. You cannot put a string in a double, because a string is not a number. Try replacing the final loop with this

P=num2str(P);
P(P=='1')="A"; 
P(P=='2')="U";
P(P=='3')="D";

P =

51×1 char array
    'D'
    'A'
    'D'
    'D'
    ...and so on

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Sebastiano Inturrisi 2018-9-6

This is perfect. Thank you! I now see why my code was producing NaN values.

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Answer 2

OCDER 2018-9-6

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You are getting NaN because you are trying to store a string value in a matrix that can only hold numeric values. See example 1 below.

If you want to store ONLY strings, then use a string array. See example 2 below.

If you want to store any type of data, like strings and numbers, then use a cell array. See example 3. below.

%Example 1 (your situation)
A = rand(1, 2);
A(1) = "A"; %NaN
A(2) = 1;   %1
%Example 2
A = strings(1, 2);
A(1) = "A"; %"A"
A(2) = 1;   %"1"
%Example 3
A = cell(1, 2);
A{1} = "A"; %"A"
A{2} = 1;   %1

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Sebastiano Inturrisi 2018-9-6

Explaining the problem this way makes things very clear. Thank you for your help!

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Answer 3

YT 2018-9-6

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Well P is of type double and you're trying to smash some strings into them, which results in NaNs. You have several options, but personally I like using cell arrays.

close all;clear all;
P = randi(3,[20 1]);
Pcell = {};
for c = 1:length(P); 
    if P(c) == 1 
        Pcell{c} = "A"; 
    elseif P(c) == 2 
        Pcell{c} = "U"; 
    else
        Pcell{c} = "D";
    end
end
%final cell
Pcell