MATLAB: In an assignment A(:) = B, the number of elements in A and B must be the same

cell array

I want to convert a cell array to a data vector, but matlab is showing this error: "In an assignment A(:) = B, the number of elements in A and B must be the same"

My code:

A = textread(['S1223.dat'],'%s');
x = zeros([size(A) 1]);
for i=1:size(A)
    x(i) = A{i};
end

I do not understand, because the vector x has the same number of rows as the cell array. How can I fix this?

Best Answer

Are the contents of the cells of A strings? Or even strings with multiple numbers in them? If so, you might have to use str2double() or sscanf().

Please see the FAQ on cell arrays: http://matlab.wikia.com/wiki/FAQ#What_is_a_cell_array.3F

Then attach S1223.dat after reading this link

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MATLAB: Help in the model!

str2num() can return a vector. str2num() is equivalent to eval() of the string surrounded by '[' and ']'. So for example if the string was '3 pi' then the '3' would get parsed as one number and the 'pi' would get parsed as the function pi() and called, returning a number, and you would get back a vector of two values where you might have been only expecting to get back the 3.

str2num() can also return an empty array -- for example if the String property is empty. Empty arrays can cause "number of elements must be the same" problems that are often not at all obvious. For example,

   a + 2 * b

will return [] if either a or b are empty. empty plus non-empty always gives an empty result.

I notice you using char() of your edit handles. If your Max property of the edit handles is 1 (the default) and if you have never stored a cell array of string in the String property, then when you get() the String property from the uicontrol('style', 'edit') then the output will be a string and you do not need to char() that (but it would not hurt.) This will be the case whether the user edited the content or not.

If, though, your Max property of the edit handles is more than 1, thereby allowing multiple lines in the edit box, then if you stored a string in the String property and the user has not modified the string, then you will get back a string for the String property. If, though, the user edited the contents when Max > 1 then even if you stored a string, you might get back a cell array of strings. Therefore, if Max > 1, it is safer to either char() the String property to force it to become char, or else cellstr() it to force it to become a cell array of string.

If you are only expecting a single numeric value in the edit box, and do not want to allow the user to enter expressions such as 'pi', then I always recommend switching to str2double(), which is more secure, and also which can handle either strings or cell array of strings (so you would not need to char() or cellstr() before calling str2double()). str2double() will return NaN if the string cannot be interpreted as a single (possibly complex) numeric value. str2double() of the empty string returns nan.

MATLAB: CSV file import in Matlab

Assuming you just want the multiple rows in the sub-cells to be converted into rows in the main array, and assuming that the main cell array is indeed a column cell vector (i.e. Nx1) and the subcells are also column cell vectors, then

if any(cellfun(@iscell, yourcellarray))
   yourcellarray = vertcat(yourcellarray{:});
end

But you'd be better off fixing the import, something we can only help with if we have an example of a file causing problem.

Even better would be to use readtable to do the parsing for you.

Best Answer

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MATLAB: Help in the model!

MATLAB: CSV file import in Matlab

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