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

set_grouping(id, val=None, bkg_id=None)
id - int or str, optional
val - array of int
bkg_id - int or str, optional

A group is indicated by a sequence of flag values starting with 1 and then -1 for all the channels in the group, following the OGIP standard.

Copy the grouping array from data set 2 into the default data set and ensure it is applied:

>>> grp = get_grouping(2) >>> set_grouping(grp) >>> group()

Copy the grouping from data set "src1" to the source and the first background data set of "src2":

>>> grp = get_grouping("src1") >>> set_grouping("src2", grp) >>> set_grouping("src2", grp, bkg_id=1) >>> group("src2")

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` .
val
This must be an array of grouping values of the same length as the data array.
bkg_id
Set to group the background associated with the 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 `val` parameter. If given two un-named arguments, then they are interpreted as the `id` and `val` parameters, respectively.

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.

References

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

Changes in CIAO

The filter is now re-calculated to match the new grouping scheme. If the data is already grouped then the filter will be displayed, so it can be reviewed to see if it remains sensible (as repeated changes to the grouping column can increase the number of noticed channels).

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

December 2023