converting characters to a number string

I'm trying to decipher a text file full of lowercase characters. First I have to convert the characters to 27 numbers (1 for each letter and 27=space) using "double". Can you guys help me code:

1. a "function" which converts any text file with 27 unique characters (including space) into a string of 27 unique numbers? I have to use "double" to convert to ASCII first, and then convert the 26 lowercase letters and space into 1:27

ex: function('hello')=[8 5 12 12 15]

2. a "function" that reverses the process, using "char"?

ex: functioninverse([8 5 12 12 15])=hello

Answer 1

[Walter Roberson]

[~, idx] = ismember( tolower(TheTextString), ['a' : 'z', ' ']);
result = double(idx);

[Erik Lee]

Thanks! How can I reverse this so char(result)=thetextstring?

[Walter Roberson]

str = ['a' : 'z', ' '];
RecalledString = str(result);

[Erik Lee]

The assignment said I have to use "char" to reverse "double"

[Walter Roberson]

str = 0 + ['a' : 'z', ' '];
RecalledString = char(str(result));