将1D阵列合并为2D阵列 [英] Merging 1D arrays into a 2D array

问题描述

是否有一个内置函数将两个1D数组连接成2D数组? 考虑一个例子:

Is there a built-in function to join two 1D arrays into a 2D array? Consider an example:

X=np.array([1,2])
y=np.array([3,4])
result=np.array([[1,3],[2,4]])

我可以想到2个简单的解决方案. 第一个非常简单.

I can think of 2 simple solutions. The first one is pretty straightforward.

np.transpose([X,y])

另一个使用lambda函数.

The other one employs a lambda function.

np.array(list(map(lambda i: [a[i],b[i]], range(len(X)))))

尽管第二个看起来更复杂，但它的速度似乎几乎是第一个的两倍.

While the second one looks more complex, it seems to be almost twice as fast as the first one.

修改 第三种解决方案涉及zip()函数.

Edit A third solution involves the zip() function.

np.array(list(zip(X, y)))

它比lambda函数快，但比@Divakar建议的column_stack解决方案慢.

It's faster than the lambda function but slower than column_stack solution suggested by @Divakar.

np.column_stack((X,y))

推荐答案

请考虑可伸缩性.如果我们增加数组的大小，那么完整的numpy命令解决方案会更快:

Take into consideration scalability. If we increase the size of the arrays, fully numpy command solutions are quite faster:

np.random.seed(1234)
X = np.random.rand(10000)
y = np.random.rand(10000)

%timeit np.array(list(map(lambda i: [X[i],y[i]], range(len(X)))))
6.64 ms ± 32.2 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
%timeit np.array(list(zip(X, y)))
4.53 ms ± 33.1 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
%timeit np.column_stack((X,y))
19.2 µs ± 30.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit np.transpose([X,y])
16.2 µs ± 247 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)
%timeit np.vstack((X, y)).T
14.2 µs ± 94.5 ns per loop (mean ± std. dev. of 7 runs, 100000 loops each)

考虑到所有建议的解决方案，当将数组的大小增加为X和y时，np.vstack(X,y).T是最快的.

Taking into account all proposed solutions, np.vstack(X,y).T is the fastest when increasing the size of arrayas X and y.

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