Data Input/Output

Data Input/Output#

This section covers how you can construct and save a Data, the class to store the table/catalogs. To use Data, you need to import it:

from pyttop.table import Data

Reading tables from files#

You can simply load the data given the path to the file and a name for the Data:

data = Data('path/to/file.fits', name='data')

And you may access the data table with the data.t property. data.t is an astropy.table.Table object: see Astropy’s documentation on Data Tables on how to use it.

Tip

A name is not mandatory when constructing a Data, but it is suggested to specify one, as the names may be used to distinguish different Data instances, generating understandable names, etc. It would usually be a good idea to set the name the same as the variable name. In case Data is initialized with a path to a file and no name is given, it will be automatically set to the file name.

You may need to specify the format of the file (especially for ascii files). For example:

data = Data(filename, format='ascii.cds', name='data')

The file is loaded with the astropy.table.Table.read() method, so refer to Astropy’s Built-In Table Readers/Writers for supported formats.

Constructing a Data from supported objects#

A Data can be created with anything that may be converted to an astropy.table.Table object, with the similar ways of constructing astropy.table.Table objects. For example:

data = Data(data_object, name='data')

The data_object may be a pandas.DataFrame, an astropy.table.Table, or anything that can be converted to astropy.table.Table with astropy.table.Table(data_object).

You may also create a Data from scratch:

data = Data(name='data')
data['col1'] = [1, 2, 3]

In general, you can construct a Data as if constructing an astropy.table.Table by simply replacing Table with Data. See Astropy’s documentation on constructing a Table for details.

Saving and loading Data#

To save a Data to a file, you can simply use the data.save() method:

data.save('path/mydata.data')

This will save the Data with PyTTOP’s built-in file format. A file with such a format can be simply loaded with:

Data.load('path/mydata.data')

Unless you are sharing your table with people that do not use PyTTOP, it is generally recommended to save Data with the built-in format, as the format preserves many properties of it (e.g., the metadata, name, row subsets), whereas most of them will be lost if you save Data with e.g. ascii, fits or any other formats.

Tip

The file extension .data is just a convention. When loading a file with the built-in format, the extension is not checked.

Exporting Data to files#

To write the Data to a file with a specified format, you can use data.save() the same way as using the write() method of an astropy.table.Table (see Astropy’s Built-In Table Readers/Writers for supported formats):

data.save('data.fits', format='fits')

Warning

PyTTOP saves relavant information in the metadata of tables and their columns. This helps with debugging and history tracking. However, the metadata may include information that you might not want to publish, such as the paths of your data in your system, operations you have performed on the data, etc. For more information on the metadata, see the documentation here. If you want to remove the metadata before exporting it for publication, you may execute:

data.meta.clear()
for coln in data.colnames: 
    data[coln].meta.clear()
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