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11.4.5. astroML.datasets.fetch_dr7_quasar

astroML.datasets.fetch_dr7_quasar(data_home=None, download_if_missing=True)

Loader for SDSS DR7 quasar catalog

Parameters :

data_home : optional, default=None

Specify another download and cache folder for the datasets. By default all scikit learn data is stored in ‘~/astroML_data’ subfolders.

download_if_missing : optional, default=True

If False, raise a IOError if the data is not locally available instead of trying to download the data from the source site.

Returns :

data : ndarray, shape = (105783,)

numpy record array containing the quasar catalog


Not all available data is extracted and saved. The extracted columns are:

sdssID, RA, DEC, redshift, mag_u, err_u, mag_g, err_g, mag_r, err_r, mag_i, err_i, mag_z, err_z, mag_J, err_J, mag_H, err_H, mag_K, err_K, specobjid

many of the objects are missing 2mass photometry.

More information at


>>> from astroML.datasets import fetch_dr7_quasar
>>> data = fetch_dr7_quasar()
>>> u_g = data['mag_u'] - data['mag_g']
>>> u_g[:3]  # first three u-g colors
array([-0.07699966,  0.03600121,  0.10900116], dtype=float32)