String to double conversion misunderstanding

I'm modifying on table imported from csv, the fields (rep.ACVoltageR), of course, are char. I try to modify the fields to double, using

tensione = str2double(rep.ACVoltageR);

but tensione is still as a char and not a double.

Were is may mistake?

>> class ACVoltageR

ans =

'char'

>> class tensione

ans =

'char'

Thanks, Fabrizio

[dpb]

How are you getting rep.ACVoltageR? If, as is implied by the reference to csv it's from a .csv file, it would be simpler to read in as numeric directly unless it is mal-formatted.

We don't have sufficient information to answer; we need the actual data how how obtained.

[Stephen23]

"I'm modifying on table imported from csv, the fields (rep.ACVoltageR), of course, are char."

Why "of course" ?

Most likely it would be much simpler and/or robust to import that numeric data correctly as numeric data. This is the approach that I strongly recommend. If you upload your data by clicking the paperclip button then we can help you with that.

"Were is may mistake?"

Possibly you tried allocating the numeric data to a table variable/column which has class character. But as you have not shown us your actual code, we will just have to guess.

[fabrizio restori]

I found my mistake, thanks to yours comments, I've better understand the import procedure (I'm new to Matlab). Now I don't need any conversion, I've just redefined data type during import.

My main error was the missuses of class function:

class ACVoltage

instead of

class (ACVoltage)

A very beginner error, worse than normally. :-(

Answer 1

[Cris LaPierre]

You are checking the class of a character array, not your variable. You need to change your syntax to check the class of your variables.

% Create a char that represents a numberic value 
rep.ACVoltageR = '4.8'

rep = struct with fields:
    ACVoltageR: '4.8'

% Convert to a double
tensione = str2double(rep.ACVoltageR)

tensione = 4.8000

% Check the class of char arrays ## incorrect syntax ##
class ACVoltageR

ans = 'char'

class tensione

ans = 'char'

% Check the class of values stored in your variables
class(rep.ACVoltageR)

ans = 'char'

class(tensione)

ans = 'double'

Answer 2

[Steven Lord]

The mistake is that you're using command form for calling the class function, not function form. These:

class ACVoltageR

ans = 'char'

class tensione

ans = 'char'

are equivalent to:

class('ACVoltageR')

ans = 'char'

class('tensione')

ans = 'char'

Also note that at this point in the execution my answer, there are no variables named ACVoltageR and tensione in the workspace!

whos ACVoltageR tensione ans % only ans is listed

  Name      Size            Bytes  Class    Attributes

  ans       1x4                 8  char               

If you want to ask for the class of the variable named tensione, use function form passing in the variable not its name.

tensione = str2double('42');
class(tensione)

ans = 'double'

whos ACVoltageR tensione ans % ans and tensione are listed, ACVoltageR still doesn't exist

  Name          Size            Bytes  Class     Attributes

  ans           1x6                12  char                
  tensione      1x1                 8  double