Changing letters to other letters with regexprep

I'm trying to change letters in a string to different ones with one line of code. I simplified my code down to the following:

regexprep('ab',{'a','b'},{'b','c'});

Ideally, this would output 'bc'. Currently, regexprep runs through the string twice and ends up outputting 'cc'.

Is there any way to prevent this from happening? Is it possible with regexprep? Also, I would prefer to keep the letters as strings, as I'm planning on using the 'preservecase' condition.

Answer 1

[Stephen23]

You don't need regexprep, using ismember and indexing is simpler:

>> str = 'a':'z'
str = abcdefghijklmnopqrstuvwxyz
>> old = 'bcd';
>> new = 'abc';
>> [X,Y] = ismember(str,old);
>> str(X) = new(Y(X))
str = aabcefghijklmnopqrstuvwxyz

Note that this works efficiently for any characters, not just a limited subset. In order to use regexprep you would probably need to use a dynamic replacement expression.

[Walter Roberson]

Well, any characters representable in the first 65536 code points ;-) If you have codepoints beyond that, such as Linear B or CJK Unified Ideograms like ? then you would need more work.

Answer 2

[OCDER]

Note that regexprep will replace things Sequentially.
regexprep('ab',{'a','b'},{'b','c'});
ab -> bb -> cc

To fix, reverse order like this:
regexprep('ab',{'b', 'a'},{'c', 'b'});
ab -> ac -> bc

[Ryoma Kawakami]

I apologize for not mentioning what I exactly planned to do after this.

I want regexprep (or something similar) to work for any shift in letters (such as 'bcd' to 'abc'), which means that reversing the order of evaluation wouldn't work.

[OCDER]

replace('a b c', {'a', 'b', 'c'}, {'c', 'a', 'b'})

Answer 3

[Walter Roberson]

 old = 'bcd';
 new = 'abc';
 lookup = char(0:255);
 lookup(old+1) = new;

 str = 'a':'z'
 str = lookup(str+1)

You do not need to add 1 if you are willing to omit the possibility of char(0) being in the string.

[Stephen23]

Interesting. This will not work for characters >255 (or whatever limit you pick).

[Walter Roberson]

Correct. You can extend it to max(str) easily, though.