content: from __future__ import print_function, division
  import numpy as np
  import matplotlib.pyplot as plt
  import vcfnp
  vcfnp.__version__
  
  filename = 'fixture/sample.vcf'
  
  # load data from fixed fields (including INFO)
  v = vcfnp.variants(filename, cache=True).view(np.recarray)
  
  # print some simple variant metrics
  print('found %s variants (%s SNPs)' % (v.size, np.count_nonzero(v.is_snp)))
  print('QUAL mean (std): %s (%s)' % (np.mean(v.QUAL), np.std(v.QUAL)))
  
  # plot a histogram of variant depth
  fig = plt.figure(1)
  ax = fig.add_subplot(111)
  ax.hist(v.DP)
  ax.set_title('DP histogram')
  ax.set_xlabel('DP')
  plt.show()
  
  # load data from sample columns
  c = vcfnp.calldata_2d(filename, cache=True).view(np.recarray)
  
  # print some simple genotype metrics
  count_phased = np.count_nonzero(c.is_phased)
  count_variant = np.count_nonzero(np.any(c.genotype > 0, axis=2))
  count_missing = np.count_nonzero(~c.is_called)
  print('calls (phased, variant, missing): %s (%s, %s, %s)'
      % (c.flatten().size, count_phased, count_variant, count_missing))
  
  # plot a histogram of genotype quality
  fig = plt.figure(2)
  ax = fig.add_subplot(111)
  ax.hist(c.GQ.flatten())
  ax.set_title('GQ histogram')
  ax.set_xlabel('GQ')
  plt.show()
  