load_ascii

Context: data

Synopsis

Load an ASCII file as a data set.

Syntax

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

Description

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.

Examples

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)

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` .
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` .

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 `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

Bugs

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