#!/usr/bin/env python
# coding: utf-8

# # Units
# 
# Testing a couple of different packages for handling units: `astropy.units`, `quantities`, and `pint`.
# 
# ## `astropy.units`
# 
# Replicating the handy [online tutorial](http://astropy.readthedocs.org/en/latest/units/).

# In[1]:


import astropy.units as u
import numpy as np


# In[16]:


42.0 * u.meter


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[1., 2., 3.] * u.m


# In[18]:


np.array([1., 2., 3.]) * u.m


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w = 42.0 * u.kilogram


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w.value


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w.unit


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dir(w)


# Variables and attributes:

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d = 2300. * u.kg/u.m**3


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d


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d.unit


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vp = 2500 * u.m/u.s


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z = vp * d


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z


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z.unit


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z.unit.compose()


# Convert velocity to ft/s: 

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from astropy.units import imperial


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vp.to(imperial.foot/u.s)


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# To put it another way:
vp * 3.28084 * (imperial.foot/u.m)


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fps = imperial.foot/u.second


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vp_imperial = vp.to(fps)
vp_imperial


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vp.cgs


# In[37]:


vp_imperial.si


# I think we could define a unit system, `oilfield` or `oil` perhaps, that has feet, g/cm^3, seconds, degF, etc.
# 
# We would also have to define various units like barrel, boe, cubic foot, etc.

# In[38]:


t = 245 * u.deg_C
t


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u.equivalencies.temperature()


# I do like how IPython plays so nicely with the formatting. 

# ## `quantities`
# 
# Potentially nice because it can also handle uncertainties. Following [the tutorial](https://pythonhosted.org/quantities/user/tutorial.html)...

# In[2]:


import quantities as pq


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vel = 2.5 * pq.km/pq.s
vel


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vel.units = pq.ft/pq.s
vel


# I think I prefer having a `to` method on the quantity object, rather than setting an attribute.
# 
# Uncertainties are quite cool, though, if rather deterministic...

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den = pq.UncertainQuantity(2850., pq.kg/pq.m**3, 75.)
den


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imp = vel * den
imp


# ## `pint`

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from pint import UnitRegistry


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ureg = UnitRegistry()


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vs = 1200. * ureg.meter/ureg.second


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vs


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vs.units


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vs.magnitude


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vs.dimensionality


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zs = vs * d
zs


# Not sure if this is good or bad, but `pint` knows about aliases and alternate spellings:

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vs.to(ureg.feet/ureg.s)


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vs.to(ureg.foot/ureg.s)


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5.0 * ureg.metres


# As with astropy, we can define units:

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ftps = ureg.foot/ureg.second
vs.to(ftps)


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t = 2245.0 * ureg.rankine
t


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t.to(ureg.degC)


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p = 4500. * ureg.psi


# In[54]:


p.to(ureg.MPa)


# ## `pint` with `numpy`

# Need to see how the units respond to being differenced, convolved, etc. 

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