In [1]:

    

import pandas as pd
import vaex as vx

%matplotlib inline


    

In [2]:

    

DATA_PATH = '../../../data/sdss_dr7_photometry_source.csv.gz'


    

In [3]:

    

def load_data(data_cols=('ra', 'dec', 'redshift'),
              filter_col='class',
              filter_val='Galaxy'):
    
    data_cols = list(data_cols)
    
    data_iter = pd.read_csv(
        DATA_PATH,
        iterator=True,
        chunksize=100000,
        usecols=data_cols + [filter_col])
    
    if filter_col is None:
        # Filtering disabled
        data = pd.concat(data_iter)
    else:
        # Filter out anything that is not a galaxy without loading the whole file into memory.
        data = pd.concat(chunk[chunk[filter_col] == filter_val]
                         for chunk in data_iter)

    return data


data = load_data()


    

In [4]:

    

data.head()


    

    
Out[4]:







  

    

      

      
ra
      
dec
      
class
      
redshift
    
  
  

    

      
3
      
196.236650
      
0.412347
      
Galaxy
      
0.617936
    
    

      
4
      
196.193644
      
0.389485
      
Galaxy
      
0.641332
    
    

      
5
      
196.220514
      
0.337969
      
Galaxy
      
0.663751
    
    

      
12
      
183.763514
      
-1.082955
      
Galaxy
      
0.390027
    
    

      
14
      
183.888350
      
-1.186661
      
Galaxy
      
0.604499
    
  

In [5]:

    

dataset = vx.from_pandas(data, name='sdss')


    

In [6]:

    

dataset.plot('ra', 'dec', what='mean(redshift)', figsize=(12,8))


    

    
Out[6]:





<matplotlib.image.AxesImage at 0x12150cbe0>






    

In [7]:

    

dataset.add_column_healpix()


    

In [8]:

    

dataset.healpix_plot(dataset.col.healpix, what='mean(redshift)',
                     show=True, healpix_input='galactic', healpix_output='galactic', figsize=(12,8))


    

    




/Users/ong017/anaconda3/envs/astro/lib/python3.5/site-packages/numpy/core/numeric.py:190: VisibleDeprecationWarning: using a non-integer number instead of an integer will result in an error in the future
  a = empty(shape, dtype, order)
/Users/ong017/anaconda3/envs/astro/lib/python3.5/site-packages/healpy/pixelfunc.py:270: RuntimeWarning: invalid value encountered in less_equal
  return np.absolute(m - badval) <= atol + rtol * np.absolute(badval)
/Users/ong017/anaconda3/envs/astro/lib/python3.5/site-packages/numpy/ma/core.py:2296: RuntimeWarning: invalid value encountered in less_equal
  mabs(xnew - value), atol + rtol * mabs(value))
/Users/ong017/anaconda3/envs/astro/lib/python3.5/site-packages/healpy/projaxes.py:998: RuntimeWarning: invalid value encountered in less
  result.data[result.data<0]=0.0
/Users/ong017/anaconda3/envs/astro/lib/python3.5/site-packages/healpy/projaxes.py:999: RuntimeWarning: invalid value encountered in greater
  result.data[result.data>1]=1.0






    

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