get_data

Context: data

Synopsis

Return details of a Sherpa data set by ID.

Syntax

get_data([id])

The get_data() function returns a variable that grants access to all the information contained in a data set by data ID. If no ID is given, then the default data set loaded in the Sherpa session is returned. The get_data() function can also be used to modify the details of a data set, e.g. to change units from "energy" to "wavelength" in a PHA grating data set, to subtract or unsubtract background data, to set the grouping of a PHA data set, among other options.

id - the id of the dataset to use; if not given, uses the default dataset id (id=1 by default, see "ahelp get_default_id")

Example 1

sherpa> get_data()

For example, data that had been read from a simple ASCII file has the following information (in this case it is the default data set, which has data id=1):

	  sherpa> print get_data()
          name      = foo.dat
          x         = Float64[124]
          y         = Float64[124]
          staterror = None
          syserror  = None

	  sherpa> print get_data(1)
          name      = foo.dat
          x         = Float64[124]
          y         = Float64[124]
          staterror = None
          syserror  = None

Example 2

sherpa> get_data("src")

The data read from a PHA file, on the other hand, has more complex information, including arrays for grouping and quality flags as well as the data (here the data set has been assigned id="src"):

	  sherpa> print get_data("src")
	  name           = s0_mar24_bin.pha
	  channel        = Int16[512]
	  counts         = Int32[512]
	  staterror      = None
	  syserror       = None
	  bin_lo         = None
	  bin_hi         = None
	  grouping       = Int16[512]
	  quality        = Int16[512]
	  exposure       = 33483.25
	  backscal       = 0.044189453125
	  areascal       = 1.0
	  grouped        = True
	  subtracted     = False
	  units          = energy
	  response_ids   = [1]
	  background_ids = []

Example 3

sherpa> get_data(3).units = "wavelength"

The get_data() function can be used to modify the details of a data set; the command in this example sets the 'units' field of the PHA grating data set 3 to "wavelength".

      sherpa> print get_data(3)
      name           = 460_leg_m1_bin10.pha
	  channel        = Int16[16384]
	  counts         = Int16[16384]
	  staterror      = None
	  syserror       = None
	  bin_lo         = Float64[16384]
	  bin_hi         = Float64[16384]
	  grouping       = Int16[16384]
	  quality        = Int16[16384]
	  exposure       = 39939.2745006
	  backscal       = 1.0
	  areascal       = 1.0
	  grouped        = True
	  subtracted     = False
	  units          = energy
	  response_ids   = [1, 2, 3]
	  background_ids = [1, 2]

      sherpa> get_data(3).units = "wavelength"

      sherpa> print get_data(3).units
      wavelength

Bugs

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