Understand if a char variable is an alphanumeric, a numeric or a string

Hi,

How can I understand if a char is an alphanumeric (a1, ab2,...), a numeric or a string ?

thanks

Answer 1

[Sean de Wolski]

doc isstrprop

Answer 2

[Azzi Abdelmalek]

   class(var) % returns a class of var

   ischar(var) % returns 1 if var is char, 0 otherwise

look at , isnan, isinf, isstruct, isnumeric,...

Answer 3

[Evan]

If a char is numeric, the following command will return false:

    isempty(str2double(s)) %where s is your char

One way I could think to see if a char is alphanumeric would be to use the following command:

    help arrayfun

So, perhaps something like this:

    arrayfun(@(x)isempty(str2double(x)),s) %where s is your char

That returns a true/false array where each element refers to a single character of your character array s. You can then compare the elements of that array to see if the char is numeric (all false), alphanumeric (mix of true and false) or a string (all true).

[Daniel Shub]

The STR2NUM function makes use of EVAL. Running EVAL on arbitrary unknown inputs is a disaster waiting to happen. At a minimum you should use STR2DOUBLE.

[Evan]

I knew that str2double is preferred in most cases where one is dealing with scalar values, but I had never actually wandered across an explanation for why this is the case. I have modified my above answer. Thanks!

Answer 4

[Walter Roberson]

I do not know what you mean by "a string" in this context. All char variables are strings in MATLAB.

"numeric" is a subset of "alphanumeric". The string '12345' is both a string of numeric characters and a string of alphanumeric characters. Your example seems to imply that you are only interested in the cases that start with alphabetic characters and end with numeric, but that is not clear. What about '123abc' or 'ab12c3' ? Do you want to include any non-Latin characters such as umlauted vowels? Accented vowels? cedilla ?

You should be considering using regexp

>> if regexp('123abc', '^[A-Za-z0-9]+$');disp('yes');else disp('no');end
yes

The ^ $ around the pattern forces a match only if the string is exactly that pattern. If the pattern does not match then regexp() will return the empty array, which "if" will consider as being false.