Creating values to a matrix with "if" statement

Question

Ivan Mich 2019-11-6

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回答： Steven Lord 2019-11-6

采纳的回答： Ruger28

Hello,

I have a .csv file which includes two columns and each column has matrix 68x1.

in order to read the file I use these commands :

clc

clear

filename1= 'myfile.csv'

[d1,tex]= xlsread(filename1);

b=d1(:,1);

I would like to take some values using the sommand "if"

I have written :

if b>=4.5&&b<60

X=2*b+5

elseif b>=60

X=3*b-6

end

but it's no use. Could anyone help me please?

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Ruger28 2019-11-6

在 MATLAB Online 中打开

if b<=4.5 && b<60

all values of b <= 4.5 are also <60. What is your logic here?

Ivan Mich 2019-11-6

Excuse me , its b>=4.5 && b<60

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Answer 1

Ruger28 2019-11-6

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编辑：Ruger28 2019-11-6

在 MATLAB Online 中打开

filename1= 'myfile.csv'
[d1,tex]= xlsread(filename1);
b = d1(:,1);
cntr = 1; % for values outside of range since no else statement
for ii = 1:length(b)
    if b(ii) >= 4.5 && b(ii) < 60
        X(cntr)=2 * b(ii) + 5;
        cntr = cntr + 1;
    elseif b(ii) >= 60
        X(cntr)=3 * b(ii) - 6;
        cntr = cntr + 1;
    end
end

Since your data might not fit all of the if statements, a counter of sorts is needed (at least that is how I would do it with your example).

You were not indexing the "b" vector at all. You need to loop through all of the variables in the vector, compare them in the if, and store them away if the current value meets your logic requirements with the counter (cntr).

Edit: forgot to index the "b" in the elseif

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Answer 2

Steven Lord 2019-11-6

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When you call if with a non-scalar expression as its condition, " An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric)." So this if statement will only execute its body if all elements of b are in the range [4.5, 60). [Actually, if b is non-scalar this should have thrown an error.]

if b>=4.5&&b<60

You could use a for loop as Ruger28 did or you could use logical indexing.