double indexing

Question

Frank 2012-1-12

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/25890-double-indexing

评论： Petter 2023-7-11

采纳的回答： Walter Roberson

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Hello,

is it possible to do double or multiple indexing in matlab? E.g.

>> v = [1,2,5,7,9]
v =
   1     2     5     7     9
>> v(1:4)
ans =
   1     2     5     7
>> v(1:4)(2:3)
ans =
   2     5

The first index create a new vector and the second index creates a new vector out of the newly created one. It is common in other languages, and it helps to avoid defining temp variables.

Cheers, Frank

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Answer 1

Walter Roberson 2012-1-12

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https://ww2.mathworks.cn/matlabcentral/answers/25890-double-indexing#answer_33898

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The closest you can get is

subsref(V(1:4), struct('type', '()', 'subs', 2:3)))

You can follow {} referencing by () referencing, {}(), but you cannot use ()() or (){} or ().{} or ().(), and you cannot use function(){} or function()() or function().field

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Frank 2012-1-12

thanks. Then I prefer to use a temp var instead. :)

Petter 2023-7-11

"You can follow {} referencing by () referencing, {}()"

This one line made my day so much easier, greatly appreciated. Thumbs up, gold star.

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Answer 2

mklcst mklcst 2014-1-23

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https://ww2.mathworks.cn/matlabcentral/answers/25890-double-indexing#answer_121917

I think it could be very useful to have a short way to perform double indexing.

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Answer 3

Jos (10584) 2014-1-23

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/25890-double-indexing#answer_121923

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If the indices are stored in variables, this is trivial!

V = [1,2,5,7,9]
ii = 1:4
jj = [2 3]
out = V(ii(jj))

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lee eugene 2019-8-2

However, if the two index do not have the same starting indexing, there would be something wrong. For example, i would like to select index [2,4] from [1,2,5,7,9] at first, and then select index [1,2]. Then it would be [2,5,7] at first and [2,5] in the end.

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