group_width

sherpa.astro.ui.group_width(id, num=None, bkg_id=None, tabStops=None)

Group into a fixed bin width.

Combine the data so that each bin contains num channels. The binning scheme is applied to all the channels, but any existing filter - created by the ignore or notice set of functions - is re-applied after the data has been grouped.

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.

  • num (int) – The number of channels to combine into a group.

  • bkg_id (int or str, optional) – Set to group the background associated with the data set. When bkg_id is None (which is the default), the grouping is applied to all the associated background data sets as well as the source data set.

  • tabStops (array of int or bool, optional) – If set, indicate one or more ranges of channels that should not be included in the grouped output. The array should match the number of channels in the data set and non-zero or True means that the channel should be ignored from the grouping (use 0 or False otherwise).

Raises

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

See also

group_adapt

Adaptively group to a minimum number of counts.

group_adapt_snr

Adaptively group to a minimum signal-to-noise ratio.

group_bins

Group into a fixed number of bins.

group_counts

Group into a minimum number of counts per bin.

group_snr

Group into a minimum signal-to-noise ratio.

set_grouping

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

set_quality

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

Notes

The function does not follow the normal Python standards for parameter use, since it is designed for easy interactive use. When called with a single un-named argument, it is taken to be the num parameter. If given two un-named arguments, then they are interpreted as the id and num parameters, respectively. The remaining parameters are expected to be given as named arguments.

Unlike group, it is possible to call group_width multiple times on the same data set without needing to call ungroup.

Unless the requested bin width is a factor of the number of channels (and no tabStops parameter is given), then some channels will be “left over”. If this happens, a warning message will be displayed to the screen and the quality value for these channels will be set to 2. This information can be found with the get_quality command.

Examples

Group the default data set so that each bin contains 20 channels:

>>> group_width(20)

Plot two versions of the ‘jet’ data set: the first uses 20 channels per group and the second is 50 channels per group:

>>> group_width('jet', 20)
>>> plot_data('jet')
>>> group_width('jet', 50)
>>> plot_data('jet', overplot=True)

The grouping is applied to the full data set, and then the filter - in this case defined over the range 0.5 to 8 keV - will be applied.

>>> set_analysis('energy')
>>> notice(0.5, 8)
>>> group_width(50)
>>> plot_data()

The grouping is not applied to channels 101 to 149, inclusive:

>>> notice()
>>> channels = get_data().channel
>>> ign = (channels > 100) & (channels < 150)
>>> group_width(40, tabStops=ign)
>>> plot_data()