The harmonic mean is defined as the reciprocal of the arithmetic mean of the reciprocals of the data, or 1 / mean(1 / x), where x contains positive numbers. Write a function harmonic_mean() with arguments x and na.rm = FALSE that gives appropriate feedback:

• It raises the warning Coercing 'x' to be numeric if x is not a numeric vector and does the coercion.
• It raises the error 'x' contains non-positive values if there are non-positive values in x. Hint: R’s function any() can also take the argument na.rm.
• It computes the harmonic mean of x in any other case, controlling for the argument na.rm.

(from: Cotton, 2013, Learning R, O’Reilly)