How to convert a subset of numpy recarray to continuous array?

Question

I have a recarray that comes from reading a csv file. I am interested in converting a subset of columns to a continuous float array. I'd like to avoid converting them to list or stacking them one by one. I tried the suggestions in https://stackoverflow.com/a/11792956 and https://stackoverflow.com/a/7842620 but I get

ValueError: new type not compatible with array.

Here is my code:

a = np.recfromcsv(r"myfile.csv")
#a has many columns of type int, float or string. I want to extract those called coeff*
coeffs_columns = [n for n in a.dtype.names if n.startswith('coeff')] 
coeffs_recarray = a[coeffs_columns]
newtype=[(n,'<f8') for n in coeffs_columns]
b = coeffs_recarray.astype(newtype)
#b is:
#array((0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0),  dtype=[('coefficients00', '<f8'), ('coefficients1', '<f8'), ('coefficients2', '<f8'), ('coefficients3', '<f8'), ('coefficients4', '<f8'), ('coefficients5', '<f8'), ('coefficients6', '<f8'), ('coefficients7', '<f8'), ('coefficients8', '<f8'), ('coefficients9', '<f8'), ('coefficients100', '<f8'), ('coefficients11', '<f8'), ('coefficients12', '<f8'), ('coefficients13', '<f8'), ('coefficients14', '<f8')])
coeffs = b.view('<f8')

The "funny" thing is that if I extract only one column, or if I work with a recarray created as

x = np.array([(1.0, 2,7.0), (3.0, 4, 9.9)], 
                 dtype=[('x', '<f8'), ('y', '<f8'), ('z', '<f8')])

the conversion works.

Unchain

Have you tried np.ascontiguousarray on your array of interest? – Copperas

Does a[coeffs_columns].view('f') work? – Tarragona

@Tarragona no, it gives the same result – Unchain

@Copperas , thanks, that has solved the problem! If you convert it to an answer I will accept it – Unchain

another "funny" thing is that coeffs_recarray.flags['C_CONTIGUOUS'] is True , but it works only if I use explicitly np.ascontguousarray – Unchain

Answer 1

Numpy provides numpy.ascontiguousarray.

This function returns a contiguous array in memory (C order) of its input array. This is especially helpful when dealing with non contiguous views on arrays.

If Fortran order is desired, use numpy.asfortranarray.

Copperas