Changing letters to other letters with regexprep

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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:
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.

Accepted Answer

Stephen23 on 28 Sep 2018
Edited: Stephen23 on 28 Sep 2018
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.
  1 Comment
Walter Roberson
Walter Roberson on 28 Sep 2018
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.

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More Answers (2)

OCDER on 28 Sep 2018
Note that regexprep will replace things Sequentially.
ab -> bb -> cc
To fix, reverse order like this:
regexprep('ab',{'b', 'a'},{'c', 'b'});
ab -> ac -> bc
OCDER on 28 Sep 2018
replace('a b c', {'a', 'b', 'c'}, {'c', 'a', 'b'})

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Walter Roberson
Walter Roberson on 28 Sep 2018
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.
Walter Roberson
Walter Roberson on 28 Sep 2018
Correct. You can extend it to max(str) easily, though.

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