Reversing parts of (even) items in a listbox (cellarray)

Question

Jason 2021-1-18

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/720140-reversing-parts-of-even-items-in-a-listbox-cellarray

编辑： Cris LaPierre 2021-1-19

Hello, I have items in a listbox (so cell array) - the integers before the "r" can be any number from 1-12.

My aim is to take any line containing an even number after r (r2, r4 etc) and reverse the other numbers and then put back into the list box

So line 2 & 4 would change to

1 2 3 r2  -> 3 2 1 r2
1 2 3 r4  -> 3 2 1 r4

This was my attempt.

               items=app.ListBoxPos.Items
                  nl=numel(items);
                  rstr=["r2","r4","r6","r8"];
                  s1=[];
                  out={};
                  for i=1:nl                      
                      line=char(items(i));
                      if contains(line, rstr)                       
                        tokens = strsplit(line, 'r' )                                                                   
                        t=fliplr(tokens{1,1})
                        new=[t,' r',tokens{1,2}]
                        app.ListBoxPos.Items{i}=new
                        %Not sure what to do now!
                      end
                  end    

Not sure if this is the most elegant way, and it falls over trying to overwrite the line in the listbox.

Thanks for any help

Jason

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Answer 1

Cris LaPierre 2021-1-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/720140-reversing-parts-of-even-items-in-a-listbox-cellarray#answer_600540

You can use mod to determine if the last number is even or not. I would then use indexing to reverse the order of the rows that end in an even number.

items=app.ListBoxPos.Items
nl=numel(items);
for i=1:nl              
  if mod(items{i}(end),2)==0
      out{i}=items{i}([end-3:-1:1 end-2:end]);
  else
      out(i)=items(i);
  end
end 
app.ListBoxPos.Items = out;

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Cris LaPierre 2021-1-19

编辑：Cris LaPierre 2021-1-19

What version of MATLAB are you using?

It's good to see you coming up with your own approach. Nice job. Just be aware that this solution suffers from the original problem - it doesn't work when the final number has 2 digits (10 or 12).

Jason 2021-1-19

Im using 2020b

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Answer 2

Jason 2021-1-19

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/720140-reversing-parts-of-even-items-in-a-listbox-cellarray#answer_601059

编辑：Jason 2021-1-19

Here is my solution based on Cris' answer:

            val = app.SNAKESCANCheckBox.Value;            
            switch val
                case 1
                  items=app.ListBoxPos.Items;
                  nl=numel(items);
                  out={};
                  for i=1:nl                    
                      L=str2num(items{i}(end));                      
                      if mod(L,2)==0                           
                         out{i}=items{i}([end-3:-1:1 end-2:end]);
                      else                          
                          out{i}=items{i};
                      end
                  end 
                  app.ListBoxPos.Items=out;
                case 0    
            end
   

I thought this worked, but when I have a number 10,11 or 12 (my numbers can be 1-12), then it doesn't quite work - Its reversing the order of the double digits

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Cris LaPierre 2021-1-19

When the number at the end is 2 characters, it would require a different approach. Perhaps finding the 'r' and using that to set the index rather the 'end'.

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