[Numpy-discussion] append_fields behavior with a (sort of) empty array

Skipper Seabold jsseabold@gmail....
Tue Mar 8 19:19:25 CST 2011


First consider this example of column_stack

import numpy as np
x = np.random.random((5,1))
y = np.random.random((5,3))

arr = np.column_stack((x[[]], y))
# this fails which is expected

arr = np.column_stack((x[:,[]], y))
# this happily works I guess because

x[:,[]]
# array([], shape=(5, 0), dtype=float64)

Now if I want to something analogous with structured array I don't see
off the bat how.  Is this desired behavior? At the very least it's a
partial bug I think.

import numpy.lib.recfunctions as nprf

xx = np.zeros(5, dtype=[('variable',float)])
xx['variable'] = np.random.random(5)

yy = np.random.random((5,2))

arr2 = nprf.append_fields((xx[[]][:], ['var1','var2'], yy.T, usemask=False)

arr2
array([(1e+20, 0.24277386045950911, 0.3801949115638894),
       (1e+20, 0.81574702386474807, 0.95094000248766541),
       (1e+20, 0.7901945469951196, 0.49315509384277167),
       (1e+20, 0.84140435880491093, 0.37125966704723368),
       (1e+20, 0.66595836283749366, 0.18154580574750145)],
      dtype=[('variable', '<f8'), ('var1', '<f8'), ('var2', '<f8')])


I think it should either fail or return yy. Surely, it shouldn't fill
in with 1e20 (ignoring fill_value). I don't think it should do any
padding if usemask=False. Am I missing something? Bug
report/enhancement ticket?

Skipper


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