[R] Help: Using vectorization method for vectors comparision

[bruclee]

I am trying to compare two sorted vectors, all elements in both vectors are
not duplicated. Ex.
a = c[5, 10, 13, 19, 23]
b = c[1, 4, 7, 9, 15]
For each element in a, i need find the max element in b which is smaller
than it, so the short answer will look like [4, 9, 9, 15, 15].
I dont want to use any loop since my real project contains element in
millions. Is there any way to speed up my operation? Many Thanks.
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