    Turn off the grouping for a PHA data set.

ungroup(id=None, bkg_id=None)
id - int or str, optional
bkg_id - int or str, optional

A PHA data set can be grouped either because it contains grouping information, which is automatically applied when the data is read in with `load_pha` or `load_data` , or because the group_xxx set of routines has been used to dynamically re-group the data. The `ungroup` function removes this grouping (however it was created).

Ungroup the data in the default data set:

>>> ungroup() >>> get_data().grouped False

Ungroup the first background component of the 'core' data set:

>>> ungroup('core', bkg_id=1) >>> get_bkg('core', bkg_id=1).grouped False

PARAMETERS

The parameters for this function are:

Parameter
Definition
id
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
Set to ungroup the background associated with the data set.

Notes

PHA data is often grouped to improve the signal to noise of the data, by decreasing the number of bins, so that a chi-square statistic can be used when fitting the data. After calling `ungroup` , anything that uses the data set - such as a plot, fit, or error analysis - will use the original data values. Models should be re-fit if `ungroup` is called; this may require a change of statistic depending on the counts per channel in the spectrum.

The grouping is implemented by separate arrays to the main data - the information is stored in the grouping and

quality arrays of the PHA data set - so that a data set can be grouped and ungrouped many times, without losing information.

The grouped field of a PHA data set is set to False when the data is not grouped.

If subtracting the background estimate from a data set, the grouping applied to the source data set is used for both source and background data sets.

References

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

See the bugs pages on the Sherpa website for an up-to-date listing of known bugs.

December 2023