iterator over a channel

        This is usefull in case of large files with a small number of channels.

        If the *raster* keyword argument is not *None* the output is
        interpolated accordingly

        Parameters
        ----------
        name : string
            name of channel
        group : int
            0-based group index
        index : int
            0-based channel index
        raster : float
            time raster in seconds
        samples_only : bool
            if *True* return only the channel samples as numpy array; if
                *False* return a *Signal* object
        raw : bool
            return channel samples without appling the conversion rule; default
            `False`

def iter_get(
        self,
        name=None,
        group=None,
        index=None,
        raster=None,
        samples_only=False,
        raw=False,
    ):
        """ iterator over a channel

        This is usefull in case of large files with a small number of channels.

        If the *raster* keyword argument is not *None* the output is
        interpolated accordingly

        Parameters
        ----------
        name : string
            name of channel
        group : int
            0-based group index
        index : int
            0-based channel index
        raster : float
            time raster in seconds
        samples_only : bool
            if *True* return only the channel samples as numpy array; if
                *False* return a *Signal* object
        raw : bool
            return channel samples without appling the conversion rule; default
            `False`

        """
        gp_nr, ch_nr = self._validate_channel_selection(name, group, index)

        grp = self.groups[gp_nr]

        data = self._load_data(grp)

        for fragment in data:
            yield self.get(
                group=gp_nr,
                index=ch_nr,
                raster=raster,
                samples_only=samples_only,
                data=fragment,
                raw=raw,
            )