get_grouping

Context: data

Synopsis

Obtain the grouping flags from a data set

Syntax

get_grouping( id [,bkg_id=None] )

The get_grouping command returns the array of grouping flags associated with a data set, by data set id. An array element set to 1 marks the beginning of a group and an element set to -1 marks subsequent members of that group. An array of grouping flags can be read from a FITS table file or column-based ASCII file and assigned to a data set with the load_grouping command, and the set_grouping command is used to actually apply a grouping scheme to a data set. The set_grouping and get_grouping commands require that the data set in question be a PHA data set.

id - the id of the data set to use (required); default=None
bkg_id - the id of the background, if the grouping is to be applied to the background data; default=None

Example 1

sherpa> get_grouping(1)

The get_grouping function retrieves the grouping scheme associated with data set id=1 (the data set id is a required argument).

Example 2

sherpa> get_grouping(2)

Here, an array of grouping flags is read from the ASCII file 'grouping.txt' and assigned to data set 2 (3c273.pi). The set_grouping function is used to actually apply the grouping scheme to data set 2, using the array which is returned by the get_grouping function.

sherpa> load_pha(2, "3c273.pi")
sherpa> load_grouping(2, "grouping.txt")
sherpa> get_grouping(2)

array([1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1, -1, -1, 1, -1, -1, -1, -1, -1, -1,..., -1, -1, -1, -1, 1, -1, -1, -1, -
1, -1, -1, -1])

sherpa> set_grouping(2, get_grouping(2))

Example 3

sherpa> get_grouping(2, 1)

The get_grouping function is used to return the array of grouping flags associated with the background of source data set 2 (bkg_id=1 represents the first background data set loaded in association with the source data set id=2).