[Numpy-tickets] [NumPy] #905: numpy.loadtxt usecols argument no longer accepts numpy arrays

[NumPy]

#905: numpy.loadtxt usecols argument no longer accepts numpy arrays
-----------------------+----------------------------------------------------
 Reporter:  rmay       |       Owner:  somebody
     Type:  defect     |      Status:  new     
 Priority:  normal     |   Milestone:  1.2.0   
Component:  numpy.lib  |     Version:  1.1.1   
 Severity:  normal     |    Keywords:  patch   
-----------------------+----------------------------------------------------
 t appears that the usecols argument to loadtxt no longer accepts numpy
 arrays:

 >>>from StringIO import StringIO
 >>>text = StringIO('1 2 3\n4 5 6\n')
 >>>data = np.loadtxt(text, usecols=np.arange(1,3))

 ValueError                                Traceback (most recent call
 last)

 /usr/lib64/python2.5/site-packages/numpy/lib/io.py in loadtxt(fname,
 dtype, comments, delimiter, converters, skiprows, usecols, unpack)
     323         first_line = fh.readline()
     324         first_vals = split_line(first_line)
 --> 325     N = len(usecols or first_vals)
     326
     327     dtype_types = flatten_dtype(dtype)

 ValueError: The truth value of an array with more than one element is
 ambiguous. Use a.any() or a.all()

 >>>data = np.loadtxt(text, usecols=np.arange(1,3).tolist())
 >>>data
 array([[ 2.,  3.],
        [ 5.,  6.]])

 Before the fix and refactoring of loadtxt in 1.1.1, converting to a list
 was not necessary.  I think the assumptions just kind of cropped in
 (exploiting certain list functionality like list.find for ease of code).

 I've attached a simple patch against HEAD that does the obvious fix and
 converts usecols to a list if it's not None.  This should allow almost any
 iterable (including tuples, which are also currently broken but used in
 the docstring) to be passed in to usecols.

-- 
Ticket URL: <http://scipy.org/scipy/numpy/ticket/905>
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