Last modified: December 2020

URL: https://cxc.cfa.harvard.edu/sherpa/ahelp/group_counts.html
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AHELP for CIAO 4.13 Sherpa v1

group_counts

Context: data

Synopsis

Group into a minimum number of counts per bin.

Syntax

group_counts(id, num=None, bkg_id=None, maxLength=None, tabStops=None)

id - int or str, optional
num - int
bkg_id - int or str, optional
maxLength - int, optional
tabStops - array of int or bool, optional

Description

Combine the data so that each bin contains `num` or more counts. 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. The background is not included in this calculation; the calculation is done on the raw data even if `subtract` has been called on this data set.


Examples

Example 1

Group the default data set so that each bin contains at least 20 counts:

>>> group_counts(20)

Example 2

Plot two versions of the 'jet' data set: the first uses 20 counts per group and the second is 50:

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

Example 3

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_counts(30)
>>> plot_data()

Example 4

If a channel has more than 30 counts then do not group, otherwise group channels so that they contain at least 40 counts. The `group_adapt` and `group_adapt_snr` functions provide similar functionality to this example. A maximum length of 10 channels is enforced, to avoid bins getting too large when the signal is low.

>>> notice()
>>> counts = get_data().counts
>>> ign = counts > 30
>>> group_counts(40, tabStops=ign, maxLength=10)

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` .
num The number of channels to combine into a group.
bkg_id 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.
maxLength The maximum number of channels that can be combined into a single group.
tabStops 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).

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_counts` multiple times on the same data set without needing to call `ungroup` .

If channels can not be placed into a "valid" group, then 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.


Bugs

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

See Also

data
copy_data, dataspace1d, dataspace2d, datastack, delete_data, fake, get_axes, get_bkg_chisqr_plot, get_bkg_delchi_plot, get_bkg_fit_plot, get_bkg_model_plot, get_bkg_plot, get_bkg_ratio_plot, get_bkg_resid_plot, get_bkg_source_plot, get_counts, get_data, get_data_contour, get_data_contour_prefs, get_data_image, get_data_plot, get_data_plot_prefs, get_dep, get_dims, get_error, get_grouping, get_quality, get_specresp, get_staterror, get_syserror, group, group_adapt, group_adapt_snr, group_bins, group_snr, group_width, load_ascii, load_data, load_grouping, load_quality, set_data, set_grouping, set_quality, ungroup, unpack_ascii, unpack_data
filtering
get_filter, ignore, ignore2d, ignore2d_id, ignore_bad, ignore_id, load_filter, notice, notice2d, notice2d_id, notice_id, set_filter, show_filter
info
get_default_id, list_data_ids, list_response_ids
modeling
clean
plotting
plot_data, set_xlinear, set_xlog, set_ylinear, set_ylog
saving
save_error, save_filter, save_grouping, save_quality, save_staterror, save_syserror
utilities
calc_data_sum, calc_data_sum2d, calc_ftest, calc_kcorr, calc_mlr, calc_model_sum2d, calc_source_sum2d, get_rate
visualization
contour, contour_data, contour_ratio, histogram1d, histogram2d, image_data, rebin