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I am not sure about the difference between (N,) and (N,1) in numpy. Assuming both are some features, they have same N dimension, and both have one sample. What's the difference?

a = np.ones((10,))
print(a.shape) #(10,)
b = np.ones((10,1))
print(b.shape) #(10,1)
jef
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    A couple of duplicates: http://stackoverflow.com/questions/22053050/difference-between-numpy-array-shape-r-1-and-r, http://stackoverflow.com/questions/38402227/numpy-why-is-there-a-difference-between-x-1-and-x-dimensionality – hpaulj Mar 19 '17 at 04:55

2 Answers2

12

In Python, (10,) is a one-tuple (the , being necessary to distinguish it from the use of parentheses for grouping: (10) just means 10), whereas (10,1) is a pair (a 2-tuple). So np.ones((10,)) creates a one-dimensional array of size 10, whereas np.ones((10,1)) creates a two-dimensional array of dimension 10×1. This is directly analogous to, say, the difference between a single number and a one-dimensional array of length 1.

ruakh
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10

The difference is that a is a one dimensional array. Like this:

[1,1,1]

And b is a multidimensinal array. Like this:

[[1],
 [1],
 [1]]
BrokenBenchmark
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el3ien
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