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QTable dtype not preserved on quantity columns

See original GitHub issue

If I attribute a column with a unit, than the datatype of the column is lost. I’ve tried on Astropy 3.0.8, 2.0.3, and 1.2.1. On astropy 1.2.1 (you probably don’t care), I cannot pull the astype trick to fix the dtype afterwards, with the error “Value not scalar compatible or convertible to an int, float or complex array”

import astropy
import astropy.table
import numpy
import sys

print('Python version: '+sys.version)
print('Astropy version: '+astropy.version.version)
print('Numpy version: '+numpy.version.version)

a = astropy.table.QTable()
b = astropy.table.QTable.Column(data=numpy.zeros(1,dtype=numpy.uint8),name='Crazy',dtype=numpy.uint8,unit='m')
a.add_column(b)
# I would expect the dtype to be uint8
# If I do not set the unit above, it will be
print(repr(a))

a['Crazy'] = a['Crazy'].astype(numpy.uint8)
print(repr(a))

I’ve tried it on two setups

Python version: 2.7.15+ (default, Oct  2 2018, 22:12:08)
[GCC 8.2.0]
Astropy version: 2.0.8
Numpy version: 1.15.0
<QTable length=1>
 Crazy
   m
float64
-------
    0.0
<QTable length=1>
Crazy
  m
uint8
-----
    0

Python version: 3.6.7 (default, Oct 22 2018, 11:32:17)
[GCC 8.2.0]
Astropy version: 3.0.3
Numpy version: 1.15.0
<QTable length=1>
 Crazy
   m
float64
-------
    0.0
<QTable length=1>
Crazy
  m
uint8
-----
    0

Issue Analytics

State:
Created 5 years ago
Comments:6 (4 by maintainers)

Top GitHub Comments

1reaction

mhvkcommented, Jan 8, 2019

Indeed, by default Quantity casts all input to float (since this makes most sense for anything with units), and thus happens when you add a Column item to your table. If you want to override this, you can do:

a['Crazy'] = astropy.units.Quantity(numpy.zeros(1,dtype=numpy.uint8), dtype=numpy.uint8)

Or, equivalently,

b = astropy.units.Quantity(numpy.zeros(1,dtype=numpy.uint8), dtype=numpy.uint8)
a.add_column(b, name='Crazy')

0reactions

astropy-bot[bot]commented, Apr 25, 2019

I’m going to close this issue as per my previous message, but if you feel that this issue should stay open, then feel free to re-open and remove the Close? label.

If this is the first time I am commenting on this issue, or if you believe I closed this issue incorrectly, please report this here