docs: def get_feature(self, ds, feat):
          """Return filtered feature data
  
          The features are filtered according to the user-defined filters,
          using the information in `ds._filter`. In addition, all
          `nan` and `inf` values are purged.
  
          Parameters
          ----------
          ds: dclab.rtdc_dataset.RTDCBase
              The dataset containing the feature
          feat: str
              The name of the feature; must be a scalar feature
          """
          if ds.config["filtering"]["enable filters"]:
              x = ds[feat][ds._filter]
          else:
              x = ds[feat]
          bad = np.isnan(x) | np.isinf(x)
          xout = x[~bad]
          return xout