Generate a comma-separated list from a numeric array?

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Eric Sampson 2013-3-20

3
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/67874-generate-a-comma-separated-list-from-a-numeric-array

评论： FM 2022-10-23

Is there a way to generate a comma-separated list from a numeric array without generating a temporary cell array? If not, would you find this functionality useful if it was added to MATLAB?

I know I would - the times that I've wanted to use this construct are very similar to the times that you use {:} with a cell array. For instance, you may have a set of n values in an array A that you want to pass to a function that takes varargin arguments. Right now if you had a cell array C you could do func( C{:} ), but you can't do func( A(someSyntax) ) . Similarly sometimes you want to be able to generate a CSL as an output argument list. Also, sometimes you might want to do B = {1, 2, C{:}, 'foo'}, which is different than B = {1, 2, A(:), 'foo'}. Lastly, you can't do things like a = 3; b=2; c=1; lol = [1 2 3]; [a b c] = deal( lol(someSyntax) )

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Matt J 2017-7-3

编辑：Matt J 2017-7-3

在 MATLAB Online 中打开

[arr.field]=deal(0)

requires no special code. However, striving for efficiency with structure and cell arrays is bound to be unfruitful. Structs and cells are inherently inefficient for storing large data, as compared to vectors and matrices, and you shouldn't really be using them in such situations. Memory access will be slow for one thing because they do not store data contiguously in RAM. If on the other hand, you don't have large data, efficiency isn't really beneficial.

Lachlan 2017-8-24

Thanks, Matt J. I hadn't noticed deal() could be used with a scalar.

I agree that matrices are far and away the most efficient where they can be used, but I was assuming that (memory inefficiency) < (memory inefficiency + interpreter inefficiency).

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采纳的回答

Matt J 2013-3-20

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/67874-generate-a-comma-separated-list-from-a-numeric-array#answer_79287

在 MATLAB Online 中打开

[a b c] = deal( lol(someSyntax) )

This one you can do, and with even easier syntax

>> [a b c] = vout(lol)
a =
       1
b =
       2
c =
       3

where vout() is defined below. You can't do it without creating a temporary cell array, but since this is hidden inside vout(), I don't see why it would matter.

function varargout=vout(C)
    if isnumeric(C), C=num2cell(C); end
    C=C(:).';
    varargout=C(1:nargout);

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Matt J 2017-1-28

编辑：Matt J 2017-1-29

The operator .' is MATLAB's transpose operator,

https://www.mathworks.com/help/matlab/ref/transpose.html

It just acts here to transpose a column cell array into a row cell array.

FM 2022-10-23

Thanks.

I find myself searching for this function again in 2022. It sure would be nice if it can be made native to Matlab. Having an extra function means one more thing that can go wrong if you don't properly sync your library of utility functions between computers, and another dependency to carry when deploying. Additionally, when posting minimal working examples online, it's more code that needs to be carried.

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