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# find index of an arry in matlab

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Rica on 12 Aug 2019
Commented: Rica on 12 Aug 2019
I have a big array and i want to find the index of the element of an array in the big array.
I know this could be easily solves with functions such find or ismember. But my goal is to give the index of the first number in the case when the the number is present more than one time in the big array like the numbers 2.2, 5.1, 6 and 7.
e.g
BigArray=[1 2 2.2 3 2.2 5 5.1 5.1 6 6 7 7.........]
ArryToBeFound=[1 2 2.2 5.1 6 7]
Solution:
index=[1 2 3 7 9 11]
Do you have any idea how to solve this?
Thank you

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### Accepted Answer

Guillaume on 12 Aug 2019
ismember is indeed the functio to use:
[~, where] = ismember(ArrayToBeFound, BigArray)
where is the index of the 1st element where the element is found, or 0, if not found. ismember guarantees that it's always the first index.

#### 1 Comment

Rica on 12 Aug 2019
next time i should read the documentation of ismember ;-)

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