[AstroPy] Constructing an astropy table with colnames and dtypes of existing table

[Aldcroft, Thomas]

On Wed, Apr 29, 2015 at 1:40 PM, Alexa Villaume <avillaum at ucsc.edu> wrote:

> Hi everybody,
>
> I’m trying to construct an astropy table using the exact same columns and
> corresponding dtypes of an existing table. The documentation goes into
> using existing columns but it wasn’t as clear to me on how to handle the
> data types. For example, I have an existing table ‘irtf’ and I want to make
> a table ‘irtf_hb’ if I do,
>
> irtf_hb = Table(names=irtf.colnames)
>
> the table is initialized with all the right column names but the dtypes
> are all floats. However, I can’t do this,
>
> irtf_hb = Table(names=irtf.colnames, dtype=irtf.dtype)
>
> Because I get an error, “ValueError: dtype must be a list or None”. I
> haven’t had any luck with trying to change the type of irtf.dtype or using
> list comprehension to extract a list of dtypes.
>
> Is there a simple way to use the dtypes of an existing table to initialize
> a new table?
>

You should be able to do:

>>> irtf_hb = Table(irtf[0:0])

This is a slight hack, but it's pretty simple and should give you a
zero-length table with all the original table properties.  I tested on a
simple case but haven't checked in detail.

In [3]: from astropy.table import Table

In [4]: t = Table([[1]])

In [5]: t2 = Table(t[0:0])

In [6]: t2
Out[6]:
<Table masked=False length=0>
 col0
int64
-----

In [7]:

- Tom


>
> Thank you,
> Alexa
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