# Hey, I am having trouble indexing into string vectors

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Andrzej Mamczura on 27 Apr 2020
Commented: Steven Lord on 27 Apr 2020
I am having trouble indexing into string arrays using logical values. As an example:
res = ["ABC" , "DEF" , "GHI"]
tf = [ 1 0 1 ]
x = res(tf)
I expect MATLAB to return
x = ["ABC" , "GHI"]
however instead i get the following error
"Array indices must be positive integers or logical values."

Sriram Tadavarty on 27 Apr 2020
Hi,
Update this as below:
res = ["ABC" , "DEF" , "GHI"]
tf = [1 0 1]; % This is of type double, so convert to logical as below
x = res(tf == 1);
Hope this helps.
Regards,
Sriram
##### 2 CommentsShowHide 1 older comment
Steven Lord on 27 Apr 2020
Many functions and pieces of functionality in MATLAB treat 1 and true as roughly equivalent and the same for 0 and false.
Indexing is not one of those pieces of functionality.
If you wanted to avoid having to compare tf each time you wanted to use it as an index, I'd create it as a logical array.
res = ["ABC", "DEF", "GHI"];
tf = [true false true]
res(tf)

Anna Case on 27 Apr 2020
tf = [1 3] is what you are looking for. If you open up the variable res, you will see "ABC" is in index 1 and "GHI" is in index 3.