I have a question regarding indexing vector elements according to their position in a sorted list. The usual query I have seen is more like this, where the secondary output of sort() is sufficient - but not for my purpose. The problem (using R2019a in Windows 10):
I have a vector (which could be arbitrarily long, with an arbitrary number of sets of replicants, each of which could have an arbitrary number of elements).
A = [20 23 1 19 20 8 5 14 9 7];
and can happily sort it:
>>B = sort(A)
B =
[1 5 7 8 9 14 19 20 20 23]
I want to create another vector C whose ith element describes the index position within B of the ith element of A. Duplicates should be handled by their original appearance order.
i.e., the desired C = [8 10 1 7 9 4 2 6 5 3]
C therefore has the properties: sort(C) = 1:size(A), and size(unique(C)) = size(C).
for ii = 1:size(A,1)
C(ii) = find(B,A(ii))
end
almost works. It doesn't handle duplicate values though, and returns C(5) = 8 instead of 9. (It's also non-vectorised and therefore presumptively ugly.)
A nastier test selection would be
>>A = [42 23 23 7 9 7 8 1 10 23 9 9 1 2 23 23 16 18 7 9];
>>B = sort(A)
B =
[ 1 1 2 7 7 7 8 9 9 9 9 10 16 18 23 23 23 23 23 42];
with corresponding
C = [20 15 16 4 8 5 7 1 12 17 9 10 2 3 18 19 13 14 6 11]
I'd appreciate any ideas on how to handle duplicates - or direction to the appropriate question/answer/function if my GoogleFu isn't up to scratch.
