text: #!/usr/bin/env python3
  # -*- coding: utf-8 -*-
  """
  Created on Tue Jan  7 22:25:54 2020
  
  @author: yuhanyao
  """
  import numpy as np
  import pandas as pd
  from astropy.table import Table
  from astropy.coordinates import SkyCoord
  
  
  df = pd.read_json("kowalski_query_result.json")
  result = df['ZTF_alerts']['(264_194758, 50_547826)']
  ndet = len(result)
  print ("In total: %d detections from ZTF alerts" %ndet)
  
  ras = np.zeros(ndet)
  decs = np.zeros(ndet)
  jds = np.zeros(ndet)
  fids = np.zeros(ndet)
  magpsfs = np.zeros(ndet)
  diffimgs = []
  for i in range(ndet):
      data = result[i]
      ras[i] = data["candidate"]["ra"]
      decs[i] = data["candidate"]["dec"]
      jds[i] = data["candidate"]["jd"]
      fids[i] = data["candidate"]["fid"]
      diffimgs.append(data["candidate"]['pdiffimfilename'])
      magpsfs[i] = data["candidate"]["magpsf"]
  diffimgs = np.array(diffimgs)
  
  ix = jds>2458484.50000 # 2019 Jan 1
  jds = jds[ix]
  decs = decs[ix]
  ras = ras[ix]
  fids = fids[ix]
  diffimgs = diffimgs[ix]
  magpsfs = magpsfs[ix]
  
  ndet = len(ras)
  print ("In 2019: %d detections from ZTF alerts" %ndet)
  
  
  tb = Table([ras, decs, fids, jds, diffimgs, magpsfs], names = ['ra', 'dec', 'fid', 'jd', 'diffimg', 'mag_alert'])
  tb.write('alert_coo.csv', overwrite=True)
          
  ra = np.median(ras)
  dec = np.median(decs)
      
  c2 = SkyCoord(ra = ra, dec = dec, unit = 'degree')
  np.savetxt('coo_kowalski.reg', [ra, dec])
  print (c2.ra.hms)
  print (c2.dec.dms)
  
  """   
  plt.plot(ras, decs, ".")
  plt.scatter(ras, decs, c = jds-min(jds))
  plt.xlim(min(ras)-0.00001, max(ras)+0.00001)
  plt.ylim(min(decs)-0.00001, max(decs)+0.00001)
  plt.colorbar()
  """ 
  
  tb = tb.to_pandas()
  tb = tb.sort_values(by ='jd')
  
  from astropy.time import Time
  jd_det = tb["jd"].values[0]
  t_det = Time(jd_det, format = "jd")
  print (t_det.datetime64)
  
  
  print ("")
  print ("alert in 2018:")
  result[2]["candidate"]
  
  
  
  