I have two sets of elements
a={3, 4.8, 5, 4.2, 3.6, 2.3, 4.5, 3.7}
b={2.8, 4.7, 5.3, 3.5, 4.7, 2.8, 4.2, 3.4}
and I create a new set which compares elements of the sets and takes their minimum
c=MapThread[Min, {a, b}]
({c=2.8, 4.7, 5, 3.5, 3.6, 2.3, 4.2, 3.4})
And now I want to find positions of elements in the new set which were changed to smaller elements. So I would like to get something like
{{1},{2},{4},{7},{8}}
Any ideas how could I do it? Thank you for any advices.
A few additional alternatives:
Position[0] @ Unitize[b-c]
Position[Alternatives @@ b] @ c
Lookup[PositionIndex @ c, DeleteDuplicates @ b, Nothing]
Map[List] @ Pick[Range @ Length @ c, Unitize[c - b], 0]
all give
{{1}, {2}, {4}, {7}, {8}}
For large input lists, the last one, or a slightly modified version of it
Map[List] @ Pick[Range @ Length @ c,Developer`ToPackedArray @ Unitize[c - b], 0]
is faster than the others.
Position[MapThread[Greater, {a, b}], True]
(* {{1}, {2}, {4}, {7}, {8}} *)
