Add new variable to table based on condition

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Blue 2019-6-26

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https://ww2.mathworks.cn/matlabcentral/answers/469053-add-new-variable-to-table-based-on-condition

评论： Adam Danz 2019-6-27

Hi,

I apologize for the newbie question but how does one add a variable to a table in Matlab based on conditions applied to other variables ?

For example, in the code below if t.y < 4 & t.y > 2 then 'A' should be stored in a new collumn t.z. Which doesnt work. Any ideas ?

y = [1 2 3 4];
x = [5 6 7 8];
t = table(x', y', 'VariableNames', {'x', 'y'})
if t.y < 4 & t.y > 2
    t.z = 'A'
end

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Bob Thompson 2019-6-27

Would using a logic index range for an undefined variable work though? I would think that if t.z didn't exist already then you would still run into the same issue Blue has. I get that the range covers a set of elements the same size as the other variables, but what values are entered for mask == 0? Do they just get created as empty? Is that allowed in a table?

Adam Danz 2019-6-27

在 MATLAB Online 中打开

Yes, mask=0 elements are merely empty strings ('')

y = [1 2 3 4];
x = [5 6 7 8];
t = table(x', y', 'VariableNames', {'x', 'y'})
mask = t.y > 2 & t.y < 4;
t.z(mask) = 'A';
t =
  4×3 table
    x    y    z
    _    _    _
    5    1     
    6    2     
    7    3    A
    8    4     