MATLAB Loop to Randomly Modify String Characters - regex

Question

I’ve started programming in MATLAB recently and tried implementing a 1337 speaker-like generator/string manipulator just for fun. As a challenge, I’m trying to randomly change the occurrence of each character so that not all “a” are changed to “#“.
It appears that my attempt works to some extend since it's very arbitrary (yet sometimes ineffective), but I believe there’s a better way of accomplishing this. Perhaps to add more alternatives for each of the 26 characters and randomly select from them, respectively?
function O = obfuscate(s)
str = 'hello world';
for i=1:length(str)
randomNum = randi(26,1);
switch randomNum
case 1
str = regexprep(str, 'a', '#', 'once');
case 2
str = regexprep(str, 'b', 'l3', 'once');
case 3
str = regexprep(str, 'c', '<', 'once');
case 4
str = regexprep(str, 'd', '|]', 'once');
case 5
str = regexprep(str, 'e', '3', 'once');
case 6
str = regexprep(str, 'f', '|#', 'once');
case 7
str = regexprep(str, 'g', '6', 'once');
case 8
str = regexprep(str, 'h', '|-|', 'once');
case 9
str = regexprep(str, 'i', '!', 'once');
case 10
str = regexprep(str, 'j', '_/', 'once');
case 11
str = regexprep(str, 'k', '|{', 'once');
case 12
str = regexprep(str, 'l', '1', 'once');
case 13
str = regexprep(str, 'm', '|\/|', 'once');
case 14
str = regexprep(str, 'n', '/\/', 'once');
case 15
str = regexprep(str, 'o', '[]', 'once');
case 16
str = regexprep(str, 'p', '|*', 'once');
case 17
str = regexprep(str, 'q', '9', 'once');
case 18
str = regexprep(str, 'r', '|2', 'once');
case 19
str = regexprep(str, 's', '$', 'once');
case 20
str = regexprep(str, 't', '+', 'once');
case 21
str = regexprep(str, 'u', '|_|', 'once');
case 22
str = regexprep(str, 'v', '\/', 'once');
case 23
str = regexprep(str, 'w', '\X/', 'once');
case 24
str = regexprep(str, 'x', '%', 'once');
case 25
str = regexprep(str, 'y', '¥', 'once');
case 26
str = regexprep(str, 'z', '2', 'once');
end
O = str;
%fprintf('%s(%i)', str(i), randomNum);
end
Any suggestions?

Answer 1

You are generating a random number between 1 and 26 but only whilst looping through the string. In your example you would only generate 11 random numbers so it is possible to never get an obfuscation whilst looping through the string.
This explains why it would be 'sometimes ineffective' as you described.
For example, in one case your random number generator could generate 10 2's in a row which would only ever change the character 'b'.
You don't have any b's in your example so none of the text will be obfuscated.
You might have more success using a map container (search for containers.map in the Matlab help) to map each character to an obfuscation (to replace your switch case logic) instead of leaving this up to probability.
You could then generate a uniform random number between e.g. 1 and 2 in each loop iteration to determine whether the character should be obfuscated.
Example:
function O = obfuscate(s)
str = 'hello world';
keys ={'h','e','l','o','w','r','d'};
values = {'|-|','3','1','[]','\X/','|2','|]'};
obfuscationMap = containers.Map(keys,values);
tempCell = {} %cell to hold the growing string
for i = 1:length(str)
randomNum = randi(2,1);
switch randomNum
case(1) %obfuscate
if(isKey(obfuscationMap, str(i)) %check key is in map to avoid missing chars
tempCell{end+1} = obfuscationMap(str(i));
else
tempCell{end+1} = str(i);
end
case(2) %don't obfuscate
tempCell{end+1} = str(i);
end
end
O = strjoin(tempStr,''); %combine cell in single string without spaces
With the above code, when randomNum is a 1, you'll get an obfuscation, if randomNum is a 2 then you won't.
So you should get obfuscations a bit more often than you were seeing previously.
You may need to modify a bit to get exactly what you want.