Return a vector of length y that is a piecewise function of x. This vector is picked as close to y (by square-distance) as possible for a set of x-only determined cut-points. Cross-validates for a good number of segments.
solve_piecewise(varName, x, y, w = NULL)
character, name of variable
numeric input (not empty, no NAs).
numeric or castable to such (same length as x no NAs), output to match
numeric positive, same length as x (weights, can be NULL)
segmented y prediction