Converting cell array to matrix

Question

Manisha Mehra 2011-3-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2369-converting-cell-array-to-matrix

采纳的回答： Walter Roberson

在 MATLAB Online 中打开

I was doing my project on huffman coding on a gray scale image. I have three arrays

code
level_of_gray
length_of_code

>> whos code

Name        Size            Bytes  Class    Attributes
code      256x1             33374  cell

>> whos level_of_gray

Name                 Size            Bytes  Class     Attributes
level_of_gray      256x1              2048  double

>> whos length_of_code

 Name                 Size            Bytes  Class     Attributes
length_of_code      256x1              2048  double

each cell of(code) has characters(strings of 0's and 1's upto length 16)

I want to make a code_dictionary=[level_of_gray;length_of_code;code]

but MATLAB is not allowing to do it. I have tried cell2mat (code). But this is also not working.

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Walter Roberson 2011-3-2

You cannot leave the codes in character representation if you want to form a numeric array. Only cell arrays can contain a mix of numbers and characters.

Manisha Mehra 2011-3-2

exactly,I don't need a numeric array.

Thanks

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Answer 1

Walter Roberson 2011-3-2

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https://ww2.mathworks.cn/matlabcentral/answers/2369-converting-cell-array-to-matrix#answer_3683

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code_dictionary = [num2cell(level_of_gray), num2cell(length_of_code), code]

This will produce a 256 x 3 cell array.

Trying to convert your code cell to matrix form is not going to work because your codes are variable length. In order to put them in to matrix form, you would have to make them all the same length, such as by padding the shorter ones with values other than 0 and 1 that the rest of your code would have to know to detect and throw away.

So what you could do is:

code_dictionary = [level_of_gray, length_of_code,
cell2mat(cellfun(@(V) [V - '0', nan(1,16-length(V))], code, 'Uniform', 0)))];

This would produce a 256 x (2+16) matrix of doubles. The first column would be the gray level, the second column would be the code length, and the 3rd to 18th columns would be the values of the code, with '0' and '1' transformed to 0 and 1, and with NaN values in all unoccupied places.