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find ID's of repeated values in array

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Kim Arnold
Kim Arnold on 17 Sep 2021
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Commented: Kim Arnoldon 17 Sep 2021
Let's say I have 2 arrays, one longer t1 (1x15 double) and a shorter one t2(1x8 double) and I tried to find the indices of t1 in the t2 as follows:
t1 = [1, 2, 3, 3, 3, 4, 5, 6);
t2=[1,1.5,2,3,4,5,6,7,8,9,9.5,19,25,31,42];
IDt1_int2=ismember(t2,t1)
>> ismember(t2,1)
ans =
1×15 logicalarray
1 0 1 1 1 1 1 0 0 0 0 0 0 0 0
but what I acutally wanted is something like this
IDt1_int2=find(ismember(t2,t1));
find(ismember(t2,t1))
ans =
1 3 4 5 6 7
but what i want it to give as an ouput is an array of IDs which considers the numbeer 3 in my t1 three times like this
[1 3 4 4 4 5 6 7];
Could you help here? Thank you
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Kim Arnold
Kim Arnold on 17 Sep 2021
Thank you very much Stephen.
Yes I tried it with
[~,idx] = ismember(t2,t1)
which was the wrong order to give the inputs.

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Accepted Answer

Simon Chan
Simon Chan on 17 Sep 2021
You may use a for loop as follows:
idx = zeros(1,length(t1));
fork = 1:length(t1)
idx(k) = find(ismember(t2,t1(k)));
end
1 Comment
Kim Arnold
Kim Arnold on 17 Sep 2021
Dear Simon,
Thanks that works perfectly fine!

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More Answers (1)

KSSV
KSSV on 17 Sep 2021
[c,ia] = ismember(t2,t1)
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Kim Arnold
Kim Arnold on 17 Sep 2021
What you wrote was correct when it was first t1 and then t2 :) however, thank you for the input
[c,ia] = ismember(t1,t2)

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