How can I change an expression like
A = (-1. a)/(x + y) - (2.1 b)/(x + y) + 4.1 + 2. x + (3. r s)/(x + y)
so that -1. a becomes a, 2. x becomes 2 x and 3. r s becomes 3 r s yet 2.1 b and 4.1 remain unchanged? Rationalize[A] almost works except it changes 2.1 b and 4.1. The expression could be even more complex.