How can I change the upper case letters in a string to lowercase while also changing the lowercase letters to uppercase?

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Pouya Rassouli
Pouya Rassouli on 19 Nov 2021
Commented: Stephen on 19 Nov 2021
I am tying to figure out how to basically make all the characters in a string change case. So all uppercase to lowercase and all lowercase to uppercase. I have tried using lower to make all capital letters lowercase, but then I run into the problem where now all the characters are lowercase so now if I go to use upper it will all become uppercase. I would like to know how to get around this, maybe not the full solution but an hint, I am thinking a for loop would be good for this, but I am not sure.

Answers (2)

Rik
Rik on 19 Nov 2021
No need for a loop.
There are three 'types' of characters that are potentially in your string:
  1. Upper case characters
  2. Lower case characters
  3. Symbols without defined case (comma, period, etc)
I would create an array that encode the type. To do this you need to create an upper case and a lower case version of your string (with upper and lower). If you use a char array instead of a string, that will allow you to do element-wise comparisons.
txt='Aa.';
upper(txt)==lower(txt)
ans = 1×3 logical array
0 0 1
That is how you can find the position of type 3. You can use a similar tactic to find type 1 and 2. Then you can use logical indexing to replace the appropriate characters.
You can also ignore type 3, since those don't change, so it doesn't matter whether you copy the 'lower case' period or the 'upper case' period.

Alex Alex
Alex Alex on 19 Nov 2021
Edited: Alex Alex on 19 Nov 2021
Try begin with this example
clc
clear
a='Hello My BROthEr'; % text in one row
for i=1:length(a)% cycle from 1 to size massive
tf=isstrprop(a(1,i),'lower');% check lower or no register in position of symbol
if tf==1% if lower
b(1,i)=upper(a(1,i));%
else % if upper
b(1,i)=lower(a(1,i));%
end
end
  1 Comment
Rik
Rik on 19 Nov 2021
==1 is not required, tf is already a scalar logical. Also, you should teach yourself the habit of using numel or size instead of length. I personally dislike using i as an index variable, as that might cause confusion or errors if at any time complex numbers are used.
Also, isstrprop allows array inputs, so you don't even need a loop at all.
Lastly, b is growing dynamically in your code. Since you know the exact size (namely size(a)), why not pre-allocate it?

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