Merge two arrays vertically to array of tuples using numpy

Question

I have two numpy arrays:

x = np.array([-1, 0, 1, 2])
y = np.array([-2, -1, 0, 1])

Is there a way to merge these arrays together like tuples:

array = [(-1, -2), (0, -1), (1, 0), (2, 1)]

Carruthers

Answer 1

In [469]: x = np.array([-1, 0, 1, 2])
In [470]: y = np.array([-2, -1, 0, 1])

join them into 2d array:

In [471]: np.array((x,y))
Out[471]: 
array([[-1,  0,  1,  2],
       [-2, -1,  0,  1]])

transpose that array:

In [472]: np.array((x,y)).T
Out[472]: 
array([[-1, -2],
       [ 0, -1],
       [ 1,  0],
       [ 2,  1]])

or use the standard Python zip - this treats the arrays as lists

In [474]: zip(x,y)   # list(zip in py3
Out[474]: [(-1, -2), (0, -1), (1, 0), (2, 1)]

Langevin

these results are not tuple data type. – Kinesiology

@johnktejik, Out[474] is a list of tuples. Out[472] isn't, but for many purposes it is just as good - including the OP's purpose(s). When creating structured arrays the distinction between a list of tuple and a list of lists is significant, but that's an exception. – Langevin

For Python 3, zip returns an iterator instead of a list. This can be converted into a list using list(zip(x,y)) – Cellarer

Answer 2

Concatenation along a second dimension may be done via np.c_[].

x = np.array([-1, 0, 1, 2])
y = np.array([-2, -1, 0, 1])

xy = np.c_[x, y]

# array([[-1, -2],
#        [ 0, -1],
#        [ 1,  0],
#        [ 2,  1]])

If you're after an array of tuples, there's the record arrays:

xy = np.rec.fromarrays([x, y])
# rec.array([(-1, -2), ( 0, -1), ( 1,  0), ( 2,  1)], dtype=[('f0', '<i4'), ('f1', '<i4')])

# convert into a list
xy.tolist()   # [(-1, -2), (0, -1), (1, 0), (2, 1)]

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