[AstroPy] Constructing Angle from a tuple specified as sign string plus numbers for degrees, arcmin, arcsec

Erik Bray embray at stsci.edu
Mon Aug 10 17:49:54 EDT 2015

On 08/10/2015 05:26 PM, Eric L. N. Jensen wrote:
> Hi all,
> I’m working with a table from CDS (i.e. from an ApJ paper) that specifies the declination coordinate in four separate columns:  a string for the sign of the declination, and three numerical columns for degrees, arcminutes, and arcseconds.  Is there a straightforward way to combine these into a single astropy.coordinates Angle object?  The standard Angle function (constructor?) only accepts a tuple with three entries.
> I guess what I’m looking for is the inverse method of ‘signed_dms’.
> If it’s of use, the table I’m working with is here:  http://iopscience.iop.org/0067-0049/184/1/18/fulltext/apjs300673t4_mrt.txt
> Thanks in advance for your help with this,

It seems a bit strange that the table format in this case indicates the sign of 
the declination as a completely separate field, rather than as just part of the 
numeric string.  But I'm not intimately familiar with the quirks of the CDS 
table format.  Is that normal?  I wonder if there's a way to get the CDS reader 
to format those fields as a single column.  Tom Aldcroft would know better.

You can instantiate an Angle array using a generator, so you could probably just 
slurp in the data using a generator expression, allowing you to transform the 
values one a time while creating the Angle rather than transforming the table 
all at once first (please bear with the LISPiness of this example):

dec = Angle(((int(row[0] + str(row[1])), row[2], row[3])
              for row in table['DE-', 'DEd', 'DEm', 'DEs'))

# (Note: originally I used row[2:] above, but there seems to be an unrelated bug 
involved in taking slices of rows...I'll report on that.)


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