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Last modified: December 2013

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AHELP for CIAO 4.9 Sherpa v1


Context: data


Return details of a Sherpa data set by 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


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

See Also

get_conf, get_covar, get_int_proj, get_int_unc, get_proj, get_reg_proj, get_reg_unc
copy_data, dataspace1d, dataspace2d, datastack, delete_data, fake, get_areascal, get_arf, get_arf_plot, get_axes, get_backscal, get_bkg, get_bkg_plot, get_bkg_scale, get_coord, get_counts, get_data_plot, get_dep, get_dims, get_error, get_exposure, get_grouping, get_indep, get_quality, get_rmf, get_specresp, get_staterror, get_syserror, group, load_ascii, load_data, load_grouping, load_quality, set_data, set_quality, ungroup, unpack_ascii, unpack_data
get_filter, load_filter, set_filter
calc_stat_info, get_fit, get_stat_info
get_default_id, list_data_ids, list_response_ids, list_stats
get_draws, get_iter_method_name, get_iter_method_opt, get_method
clean, get_model, get_model_component, get_model_component_image, get_model_component_plot, get_model_plot, get_num_par, get_order_plot, get_par, get_pileup_model, get_response, get_source, get_source_component_image, get_source_component_plot, image_source
get_split_plot, plot_data, set_xlinear, set_xlog, set_ylinear, set_ylog
get_kernel, get_psf
save_error, save_filter, save_grouping, save_quality, save_staterror, save_syserror
get_chisqr_plot, get_delchi_plot, get_prior, get_sampler, get_stat
calc_data_sum, calc_data_sum2d, calc_ftest, calc_kcorr, calc_mlr, calc_model_sum2d, calc_source_sum2d, get_analysis, get_rate
contour, contour_data, contour_ratio, get_ratio, get_resid, histogram1d, histogram2d, image_data, image_getregion, rebin

Last modified: December 2013
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