How to check if several variables exist and assign a value to non-existing variables?

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Carlos HM
Carlos HM on 23 Jun 2018
Commented: Stephen on 18 Apr 2020
I am trying to check if several variables exist, and assign a value to those of them who do not exist.
a=7;
e=4;
nums=["a", "b", "c", "d", "e", "f"];
i=1;
while i<=length(nums)
if exist(nums(i),'var')==0
eval(nums(i))=i;
end
i=i+1;
end
b, c, d and f do not exist before the while loop, so they should get assigned a value. But it doesn't work, I get the following error:
Function 'subsindex' is not defined for values of class 'string'.
Thank you for your help.

Accepted Answer

Rik
Rik on 23 Jun 2018
Replacing bij chars arrays makes it work, although I wonder about eval. It's generally a bad idea, but I don't see a good alternative without knowing the context that you plan to use this in.
a=7;
e=4;
nums=['a', 'b', 'c', 'd', 'e', 'f'];
i=1;
while i<=length(nums)
if exist(nums(i),'var')==0
eval([nums(i) '=i;'])
end
i=i+1;
end
  1 Comment
Walter Roberson
Walter Roberson on 23 Jun 2018
a=7;
e=4;
nums={'a', 'b', 'c', 'd', 'e', 'f'};
i=1;
while i<=length(nums)
if exist(nums{i},'var')==0
eval([nums{i} '=i;'])
end
i=i+1;
end
or
a=7;
e=4;
nums=["a", "b", "c", "d", "e", "f"];
i=1;
while i<=length(nums)
if exist(nums(i),'var')==0
eval([nums(i) + '=' + i]);
end
i=i+1;
end

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