get_grouping

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.

Parameters
  • 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.

Returns

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 (is is a reference to the values used to define the quality, not a copy).

Return type

ndarray or None

Raises

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

See also

fit()

Fit one or more data sets.

get_quality()

Return the quality array for a PHA data set.

ignore_bad()

Exclude channels marked as bad in a PHA data set.

load_grouping()

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

set_grouping()

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

Notes

The meaning of the grouping column is taken from 1, 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.

References

1

“The OGIP Spectral File Format”, https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/spectra/ogip_92_007/ogip_92_007.html

Examples

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)