Used internally, to find the index of the value in a vector nearest to a target value, possibly in a specific preferred direction.
which_nearest(values, target, dir)Single integer, the index of the value closest to target according
to dir.
numeric vector, the values considered.
single numeric value, the target to find the value closest to.
single numeric value. If 0 (the default), finds the index of the
value closest to the target, regardless of the direction. If < 0 or
> 0, finds the index of the value closest to the target, but only
considers values at or below/above target, respectfully, if any (otherwise
returns the closest value regardless of direction).