SkyCoord.reshape Speed Test

reshape_skycoord_timing.py

from __future__ import print_function, division

import timeit
import numpy as np

# First, test how long it takes to reshape a numpy array

repeat = 20
number = 100000

setup = """
import numpy as np
shape = (20,10,3)
s = (shape[0]*shape[1], shape[2])
"""

stmt = """
x = np.random.random(shape)
x.shape = s
"""
t1 = np.percentile(timeit.repeat(setup=setup, stmt=stmt, repeat=repeat, number=number), 5.) / number

stmt = """
x = np.random.random(shape)
"""
t0 = np.percentile(timeit.repeat(setup=setup, stmt=stmt, repeat=repeat, number=number), 5.) / number

print(('numpy.ndarray timings\n'
       '=========================\n'
       '        random: {:.4f} ms\n' +
       'random+reshape: {:.4f} ms\n' +
       '    difference: {:.4f} ms'
      ).format(1.e3*t0, 1.e3*t1, 1.e3*(t1-t0)))

# On my laptop, I get:
#
#         random: 0.0069 ms
# random+reshape: 0.0073 ms
#     difference: 0.0004 ms
#
# I think the 0.0004 ms is indistinguishable from noise (e.g., the real time may be much less).


# Next, test how long it takes to reshape a SkyCoord

repeat = 10
number = 50

setup = """
import numpy as np
from astropy.coordinates import SkyCoord
import astropy.units as u
shape = (20,10,3)
s = (shape[0]*shape[1], shape[2])
"""

stmt = """
l = np.random.random(shape)
b = np.random.random(shape)
c = SkyCoord(l*u.deg, b*u.deg, frame='galactic')
c2 = c.reshape(s)
"""

t1 = np.percentile(timeit.repeat(setup=setup, stmt=stmt, repeat=repeat, number=number), 5.) / number

stmt = """
l = np.random.random(shape)
b = np.random.random(shape)
c = SkyCoord(l*u.deg, b*u.deg, frame='galactic')
"""
t0 = np.percentile(timeit.repeat(setup=setup, stmt=stmt, repeat=repeat, number=number), 5.) / number

print(('SkyCoord timings\n'
       '=========================\n'
       '        random: {:.4f} ms\n' +
       'random+reshape: {:.4f} ms\n' +
       '    difference: {:.4f} ms'
      ).format(1.e3*t0, 1.e3*t1, 1.e3*(t1-t0)))

# On my laptop, I get:
#
#         random: 15.2013 ms
# random+reshape: 47.2483 ms
#     difference: 32.0470 ms
#
# On my laptop, changing the size of the input coordinates from 600 to 6
# does not change the answer, so there appears to be some size-independent
# overhead of about 30 ms in SkyCoord.reshape.