How to extract indices with a condition?

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Mr M.
Mr M. 2018-3-26
评论： Walter Roberson 2024-2-29
For example I have Y = X(X==42), but I need the indices also!
  2 个评论
Stephen23
Stephen23 2018-3-26
X==42 gives the logical indices, which will be faster than using find.
rbih rbih
rbih rbih 2020-6-12
hi Mr M. i just wondering about the value that you're searching index for (42), isn't that related to the quiz of rigid body kinematics course (Concept Check 9 - Euler Angle Differential Kinematic Equations) on coursera!
just for fun, have a good day.

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采纳的回答

Birdman
Birdman 2018-3-26
编辑：Birdman 2018-3-26
To find the index where X is equal to 42, type
idx=find(X==42)
Y=X(idx)

更多回答（1 个）

Walter Roberson
Walter Roberson 2018-3-26
find(X==42) and store in a variable. Then X(that_variable)
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显示 8更早的评论
Ron
Ron 2024-2-29
@Rik, thanks for replying. Yes my comment was somewhat arbitrary here. Yes I was talking about "X(setdiff(1:numels(X), ind0))", this statement. I couldnt understand what it means. Yes you are right about the typo, thanks for correcting me.
Walter Roberson
Walter Roberson 2024-2-29
setdiff(1:numels(X), ind0)
returns all the indices of X that do not appear in ind0
It is questionable whether this will be any faster than
X(X ~= 0)
but the original poster wanted a different way.

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