get error when remove an item

Question

huda nawaf 2012-3-2

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hi, i want to remove an item from array, but get error

this is my code

align(1,:)='asd-as---tyr';
align(2,:)='fg--ds--h-ty';
for i=1:12
  if align(1,i)=='-' & align(2,i)=='-'
     align(1,i)=[];  align(2,i)=[];
  end
end
      ??? A null assignment can have only one non-colon index.
Error in ==> testt at 6
            align(1,i)=[];

thanks in advance

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Answer 1

Jan 2012-3-2

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When you remove a character, the string is getting shorter. But the FOR-loop tries to access all characters of the initial size.

Either run the loop in reverse direction:

align(1,:) = ['asd-as---tyr'; ...
              'fg--ds--h-ty'];
for i=12:-1:1
  if align(1,i)=='-' & align(2,i)=='-'
    align(:,i) = [];
  end
end

Or use a vectorized approach, which is faster and nicer:

align(align(1, :)=='-' & align(2, :)=='-', :) = []; % No FOR loop, no IF

[EDITED]: Typo in the line above (thanks Walter!):

align(:, align(1, :)=='-' & align(2, :)=='-') = [];

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Walter Roberson 2012-3-2

align(:, align(1, :)=='-' & align(2, :)=='-') = []; % No FOR loop, no IF

huda nawaf 2012-3-2

many many thanks walter

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Answer 2

Aurelien Queffurust 2012-3-2

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To remove the minus sign you could use:

align= char(strrep(align(1,:),'-','') ,strrep(align(2,:),'-','') )

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Answer 3

the cyclist 2012-3-2

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I can see how you would find that error message a bit cryptic, but here is what is going on.

Your variable align is a 2x12 character array. With your line of code

align(1,i)=[];

is going to attempt to remove the upper-left corner of that array. But MATLAB can't do that. There cannot be a character array that has one row of 11 elements, and a second row that is 12 elements. One element cannot be "empty" in that way. (That is what error message is saying.) You can only do the null assignment for a whole row or column at once.

So, in your case, you could combine your two null assignment statements into the single statement

align(:,i) = [];

and MATLAB will delete the i'th column, in its entirety.

Be aware that your array align is going to keep getting trimmed, as it goes through the for loop, so it will no longer be width 12.