Cell arrays and the unique function

Question

Jess 2013-3-19

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https://ww2.mathworks.cn/matlabcentral/answers/67873-cell-arrays-and-the-unique-function

采纳的回答： Cedric

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Hi all,

Working on some code to remove cell arrays so I can convert the code to C using Matlab Coder.

Just wondering what the right way of going about it would be for something like this:

myvalues = unique({input_x.(my_name)});

The input is a cell array, so the unique function also returns a cell array, neither of which I want. Any pointers of how to go about this to remove the cell arrays would be appreciated.

Thanks

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Answer 1

Cedric 2013-3-20

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https://ww2.mathworks.cn/matlabcentral/answers/67873-cell-arrays-and-the-unique-function#answer_79286

编辑：Cedric 2013-3-20

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You can proceed as follows:

 >> c = {1, 2, 3, 4}
 c = 
    [1]    [2]    [3]    [4]
 >> [c{:}]
 ans =
     1     2     3     4

It is applied to struct arrays as follows:

 >> input_x = struct('a', {7,8,9,5,4,3}) ;
 >> [input_x.a]
 ans =
     7     8     9     5     4     3

or, if the fieldname is not static

 >> [input_x.('a')]
 ans =
     7     8     9     5     4     3

In fact, c{:} is a comma-separated list (the same that you have when you define columns of an array, or when you list arguments in function calls), so the outcome of "square-bracketting" it is an array. It is something quite useful when you want to pass elements of a cell array to a function as if you were listing arguments separated by commas. To illustrate..

 function myPrintf(format, varargin)
    % do something..
    fprintf(format, varargin{:}) ;
 end

Calling

myPrintf('Name:%s, age:%d, streetNo:%d\n', 'John', 40, 12) ;

leads to varargin = {'John', 40, 12}, and using it as a comma-sep. list with varargin{:} in the call to FPRINTF is indeed performing the following call

fprintf('Name:%s, age:%d, streetNo:%d\n', 'John', 40, 12) ;

.. it's the to some extent the MATLAB way for managing cases where you'd use a vector function in C, e.g. vfprintf ..