Last modified: December 2023

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AHELP for CIAO 4.16 Sherpa


Context: data


Load an ASCII file as a data set.


load_ascii(id, filename=None, ncols=2, colkeys=None, dstype=Data1D,
sep=' ', comment='#')

id - int or str, optional
filename - str
ncols - int, optional
colkeys - array of str, optional
sep - str, optional
comment - str, optional
dstype - optional


The standard behavior is to create a single data set, but multiple data sets can be loaded with this command, as described in the `sherpa.astro.datastack` module.


Example 1

Read in the first two columns of the file, as the independent (X) and dependent (Y) columns of the default data set:

>>> load_ascii('sources.dat')

Example 2

Read in the first three columns (the third column is taken to be the error on the dependent variable):

>>> load_ascii('sources.dat', ncols=3)

Example 3

Read in from columns 'RMID' and 'SUR_BRI' into data set 'prof':

>>> load_ascii('prof', 'rprof.dat',
...            colkeys=['RMID', 'SUR_BRI'])

Example 4

The first three columns are taken to be the two independent axes of a two-dimensional data set ( x0 and x1 ) and the dependent value ( y ):

>>> load_ascii('fields.txt', ncols=3,
...            dstype=Data2D)

Example 5

When using the Crates I/O library, the file name can include CIAO Data Model syntax, such as column selection. This can also be done using the colkeys parameter, as shown above:

>>> load_ascii('prof',
...            'rprof.dat[cols rmid,sur_bri,sur_bri_err]',
...            ncols=3)


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` .
filename The name of the file to read in. Selection of the relevant column depends on the I/O library in use (Crates or AstroPy).
ncols The number of columns to read in (the first ncols columns in the file). The meaning of the columns is determined by the dstype parameter.
colkeys An array of the column name to read in. The default is none .
sep The separator character. The default is ' ' .
comment The comment character. The default is '#' .
dstype The data class to use. The default is `Data1D` .


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 `filename` parameter. If given two un-named arguments, then they are interpreted as the `id` and `filename` parameters, respectively. The remaining parameters are expected to be given as named arguments.

The column order for the different data types are as follows, where x indicates an independent axis and y the dependent axis.

Identifier Required Fields Optional Fields
Data1D x, y statistical error, systematic error
Data1DInt xlo, xhi, y statistical error, systematic error
Data2D x0, x1, y shape, statistical error, systematic error
Data2DInt x0lo, x1lo, x0hi, x1hi, y shape, statistical error, systematic error


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

See Also

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_quality, get_specresp, get_staterror, get_syserror, group, group_adapt, group_adapt_snr, group_bins, group_counts, group_snr, group_width, load_arf, load_arrays, load_ascii_with_errors, load_bkg, load_bkg_arf, load_bkg_rmf, load_data, load_grouping, load_image, load_multi_arfs, load_multi_rmfs, load_pha, load_quality, load_rmf, load_staterror, load_syserror, load_table, pack_image, pack_pha, pack_table, set_data, set_quality, ungroup, unpack_arf, unpack_arrays, unpack_ascii, unpack_bkg, unpack_data, unpack_image, unpack_pha, unpack_rmf, unpack_table
get_filter, load_filter, set_filter
get_default_id, list_bkg_ids, list_data_ids, list_response_ids
add_model, add_user_pars, clean, load_table_model, load_template_interpolator, load_template_model, load_user_model, save_model, save_source
plot_data, set_xlinear, set_xlog, set_ylinear, set_ylog
save_arrays, save_data, save_delchi, save_error, save_filter, save_grouping, save_image, save_pha, save_quality, save_resid, save_staterror, save_syserror, save_table
calc_data_sum, calc_data_sum2d, calc_ftest, calc_kcorr, calc_mlr, calc_model_sum2d, calc_source_sum2d, get_rate
contour, contour_data, contour_ratio, histogram1d, histogram2d, image_data, rebin