'Resolve the baseline field selector
@param baseline: the baseline selector'

def resolve_baseline(self, baseline):

    resource = self.resource
    rfields = self.rfields
    baseline_rfield = None
    if baseline:
        try:
            baseline_rfield = resource.resolve_selector(baseline)
        except (AttributeError, SyntaxError):
            baseline_rfield = None
    if (baseline_rfield and (baseline_rfield.ftype not in NUMERIC_TYPES)):
        current.log.error(('Invalid    field    type    for    baseline:    %s    (%s)' % (baseline, baseline_rfield.ftype)))
        baseline_rfield = None
    rfields['baseline'] = baseline_rfield
