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Is there an implementation where I can join two arrays based on their keys? Speaking of which, is the canonical way to store keys in one of the NumPy columns (NumPy doesn't have an 'id' or 'rownames' attribute)?
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Use numpy. concatenate() to merge the content of two or multiple arrays into a single array. This function takes several arguments along with the NumPy arrays to concatenate and returns a Numpy array ndarray. Note that this method also takes axis as another argument, when not specified it defaults to 0.
NumPy's concatenate function can be used to concatenate two arrays either row-wise or column-wise. Concatenate function can take two or more arrays of the same shape and by default it concatenates row-wise i.e. axis=0. The resulting array after row-wise concatenation is of the shape 6 x 3, i.e. 6 rows and 3 columns.
Stack arrays in sequence vertically (row wise). This is equivalent to concatenation along the first axis after 1-D arrays of shape (N,) have been reshaped to (1,N).
+ operator can be used to merge two lists. Lists can be merged like this in python.
If you want to use only numpy, you can use structured arrays and the lib.recfunctions.join_by function (see http://pyopengl.sourceforge.net/pydoc/numpy.lib.recfunctions.html). A little example:
In [1]: import numpy as np
...: import numpy.lib.recfunctions as rfn
...: a = np.array([(1, 10.), (2, 20.), (3, 30.)], dtype=[('id', int), ('A', float)])
...: b = np.array([(2, 200.), (3, 300.), (4, 400.)], dtype=[('id', int), ('B', float)])
In [2]: rfn.join_by('id', a, b, jointype='inner', usemask=False)
Out[2]:
array([(2, 20.0, 200.0), (3, 30.0, 300.0)],
dtype=[('id', '<i4'), ('A', '<f8'), ('B', '<f8')])
Another option is to use pandas (documentation). I have no experience with it, but it provides more powerful data structures and functionality than standard numpy, "to make working with “relational” or “labeled” data both easy and intuitive". And it certainly has joining and merging functions (for example see http://pandas.sourceforge.net/merging.html#joining-on-a-key).
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