Indexing of a size() object

Question

Adrian Valente 2020-11-27

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链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/665438-indexing-of-a-size-object

编辑： Stephen23 2020-11-27

采纳的回答： Ameer Hamza

Hello,

If I have an array named arr, and run the following:

size(arr)(1)

then I get an error: "Indexing with parentheses '()' must appear as the last operation of a valid indexing expression."

However when adding an intermediate step:

s = size(arr);
s(1)

then everything runs as expected. So I don't have a practical problem to solve here, but was curious to know more about the reasons for that behavior, and when indexing should not be used.

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Stephen23 2020-11-27

编辑：Stephen23 2020-11-27

Note that

size(arr,1)

would be the MATLAB way to measure the first dimension of an array.

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Answer 1

Ameer Hamza 2020-11-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/665438-indexing-of-a-size-object#answer_557958

编辑：Ameer Hamza 2020-11-27

Unlink some other languages, such a chain of indexing is not supported in MATLAB. You can find the discussion on this issue on the following links

https://stackoverflow.com/questions/3627107/how-can-i-index-a-matlab-array-returned-by-a-function-without-first-assigning-it

https://www.mathworks.com/matlabcentral/answers/78242-indexing-of-fresh-array-in-one-line-without-intermediate-variable

I guess one of the main reasons it is still not supported is because of the ambiguity between the function call and indexing. Both use pranthesis (). If Mathworks make the decision to support this now, it can make the program slow and make it difficult for the JIT compiler to improve the speed.