error converting chars to string

Hi folks,

I keep getting an error when running the following line of code:

Names = xml2struct([TestFolder '\captureSettings.xml']);
NumbOfSamples = str2double(Names.Children(20).Children.Data);
    
for m = 1:NumbOfSamples
    Name        = Names.Children(22).Children(2*m).Children(4).Children.Data;
    Samples(m)  = convertCharsToStrings(regexprep(Name, '\s+', ''));
end

The error is:

The following error occurred converting from string to cell:
Conversion to cell from string is not possible.

I can't seem to find why this error appears.Any thoughts on this would be much appreciated!

Thanks in advance!

Answer 1

[Adam Danz]

Assuming Samples is a cell array

Samples{m}  = convertCharsToStrings(regexprep(Name, '\s+', ''));
%      ^ ^

If Samples isn't predefined, don't forget to preallocate it:

Samples = cell(1,NumbOfSamples);
for m = 1:NumbOfSamples
    ...
end

As dpb mentioned, if you're using strings instead of char vectors,

Samples = strings(1,NumbOfSamples);
%         ^^^^^^^
for m = 1:NumbOfSamples
    Name        = Names.Children(22).Children(2*m).Children(4).Children.Data;
    Samples(m)  = convertCharsToStrings(regexprep(Name, '\s+', ''));
    %      ^ ^
end

[Teshan Rezel]

perfect, thank you! Just the curly brackets I needed!

[dpb]

That makes it run, but why are you embedding a string variable into a cell?

>> Samples{1}=convertCharsToStrings(regexprep({'Freddy Mae'},'\s+',''))
Samples =
  1×1 cell array
    {["FreddyMae"]}
>> 

Just use the array of strings or don't convert the output to a string if going to use cell strings.

[Adam Danz]

Thanks, dpb, good catch. The string class has been out for 4+ years and I still mainly think in chars 🙄.

[dpb]

strings have their place, but they're also limited in their syntax.

One of my pet peeves is the only way to get a substring is to cast back to char() by cell curlies dereferencing notation...

For the above example

>> Samples(1)=convertCharsToStrings(regexprep({'Freddy Mae'},'\s+',''))
Samples = 
    "FreddyMae"
>> Samples(1:2)
Index exceeds array bounds. 
>> Samples{1:2}
Index exceeds array bounds. 
>> Samples{1}(1:2)
ans =
    'Fr'
>> 

but then it returns a char() string instead of the string variable class which you then have to either convert or remember to use character indexing unless you directly store the result into a string variable; then the typecast does occur on assignment. But, temporaries aren't, so you can end up with syntax errors to fix.

And there's no substring() function to abstract to higher level. Seems to be a new class that is let into the wild before being fully developed.

Answer 2

[dpb]

You've previously defined Samples as a cell array (either deliberately or by accident) --

>> Samples={}
Samples =
  0×0 empty cell array
>> Samples(1)=convertCharsToStrings(regexprep({'Freddy Mae'},'\s+',''))
The following error occurred converting from string to cell:
Conversion to cell from string is not possible. 
>> 

Further examination reveals:

>> Samples=[]
Samples =
     []
>> Samples(1)=convertCharsToStrings(regexprep({'Freddy Mae'},'\s+',''))
Samples =
           NaN
>> Samples=string("")
Samples = 
    ""
>> Samples(1)=convertCharsToStrings(regexprep({'Freddy Mae'},'\s+',''))
Samples = 
    "FreddyMae"
>>