[Numpy-discussion] unpack argument in loadtxt/genfromtxt does not work as documented

Chris Fonnesbeck fonnesbeck@gmail....
Wed Oct 6 21:48:16 CDT 2010

The documentation for loadtxt and genfromtxt state that the unpack
argument functions as follows:

If True, the returned array is transposed, so that arguments may be
unpacked using x, y, z = loadtxt(...).

In practice, this does not always occur. I have a csv file of mixed
data types, and try importing it via:

genfromtxt("progestogens.csv", delimiter=",", names=True,
dtype=dtype([('id', int),('study', '|S25'),('year', int),('treat',
int),('drug', '|S25'),('form', '|S10'),('ptb', int),('mgest',
int),('lab', int),('n', int),('y', int),('var', '|S5'),('wt',
int),('sdwt', int)]), unpack=True)

With unpack=True, I would expect the data to be presented by columns,
however the resulting array is by rows:

array([(1, 'Meis', 2003, 1, '17P', 'IM', 1, 0, 0, 306, 111, 'ptb'),
       (1, 'Meis', 2003, 0, '17P', 'IM', 1, 0, 0, 153, 84, 'ptb'),
       (2, 'Rai', 2009, 1, 'Progesterone', 'Oral', 1, 0, 0, 74, 29, 'ptb'),
       (2, 'Rai', 2009, 0, 'Progesterone', 'Oral', 1, 0, 0, 74, 44, 'ptb'),

The same behaviour occurs using loadtxt. Moreover, this array is
untransposeable, so I am stuck with having to iterate over all the
rows, making genfromtxt no better than csv.reader.

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