sherpa.astro.ui.get_grouping(id=None, bkg_id=None)

Return the grouping array for a PHA data set.

The function returns the grouping value for each channel in the PHA data set.

  • id (int or str, optional) – The identifier for the data set to use. If not given then the default identifier is used, as returned by get_default_id.

  • bkg_id (int or str, optional) – Set if the grouping flags should be taken from a background associated with the data set.


grouping – A value of 1 indicates the start of a new group, and -1 indicates that the bin is part of the group. This array is not filtered - that is, there is one element for each channel in the PHA data set. Changes to the elements of this array will change the values in the dataset (it is a reference to the values used to define the quality, not a copy).

Return type:

ndarray or None


sherpa.utils.err.ArgumentErr – If the data set does not contain a PHA data set.

See also


Fit one or more data sets.


Return the quality array for a PHA data set.


Exclude channels marked as bad in a PHA data set.


Load the grouping scheme from a file and add to a PHA data set.


Apply a set of grouping flags to a PHA data set.


The meaning of the grouping column is taken from the OGIP standard which says that +1 indicates the start of a bin, -1 if the channel is part of group, and 0 if the data grouping is undefined for all channels.


K. A. Arnaud, I. M. George & A. F. Tennant, “The OGIP Spectral File Format”


Copy the grouping array from the default data set to data set 2:

>>> grp1 = get_grouping()
>>> set_grouping(2, grp1)

Return the grouping array of the background component labelled 2 for the ‘histate’ data set:

>>> grp = get_grouping('histate', bkg_id=2)