Find the position of numbers in array

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Marco Piazza
Marco Piazza on 30 Sep 2022
Edited: Ergin Sezgin on 30 Sep 2022
Hello everybody, I'm trying to find the position of some values in an array. The values i'm interested in are in a 1x182 vector and I want to find they're position in a 1x1820 vector (practically I'm just looking for a percentile). Can you guess how I can find them?
PS: i did it with a for loop using the find function but i think it is a non-efficient way, there must be an easier and fast way!
Thank a lot in advance,

Answers (3)

Walter Roberson
Walter Roberson on 30 Sep 2022
percent_present = mean(ismember(SmallVector, LargeVector)) * 100

Star Strider
Star Strider on 30 Sep 2022
I am not certain what you are asking.
Perhaps using the ismember (or ismembertol) function will do what you want.
Star Strider
Star Strider on 30 Sep 2022
Getting them is straightforward. Getting them in that exact order requires a bit of coding gymnastics —
a = [4 5 7 2 1 6 3 9 8];
b = [2 7 8];
[~,idx] = ismember(a, b);
[idx_sorted,sortidx] = sort(idx(idx>0));
idx2 = find(idx);
Result = idx2(sortidx)
Result = 1×3
4 3 9

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Ergin Sezgin
Ergin Sezgin on 30 Sep 2022
Edited: Ergin Sezgin on 30 Sep 2022
Hello Marco,
Following code might help with your task:
inputArray = 100*rand(1,1820); % you should use your array
selectedElems = randperm(1820,182); % random indexing for subset,
yourVector = inputArray(selectedElems); % you should use your vector instead
elemPositions = zeros(size(yourVector)); % result vector for determined positions
for i=1:size(yourVector,2)
elemPositions(1,i) = find(inputArray==yourVector(1,i));
isequal(selectedElems, elemPositions) % Compare real and determined positions
ans = logical
Good luck





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