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efueyo
Asked: 2020-08-10 07:44:29 +0800 CST 2020-08-10 07:44:29 +0800 CST

Nested lists result in multidimensional arrays

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I don't understand this way to initialize a multidimensional array using a list of lists (Numpy):

np.array([range(i, i + 3) for i in [2, 4, 6]])

OUT:

array([[2, 3, 4],
       [4, 5, 6],
       [6, 7, 8]])

How do you get 3, 5, 7 and 4, 6, 8?

I understand that with range(i, i+3) you are defining that the matrix will have three columns, but how can we understand in this code, that the values ​​of each of the two columns are obtained by adding 1 to the value of the previous column ?.

numpy

1 Answers

  1. Best Answer

    The false appearance that 1 is being added, is made by the range()and the chosen numbers. What you are doing is the following:

    1. With the loop forwe take the first number in the list the two
    2. We define a range from two to five [2, 2 + 3).
    3. This returns us a list with rank two to five: [2,3,4]. We have the first row

    Once this is done, we repeat the same loop again.

    The forbrings us the next number in the list, in this case four , we create a range from four to seven and it returns us a list [4,5,6]. We have the second row.

    Finally we would start the loop again with the last number six and at the end we would get the third and last row: [6,7,8].

    range() function

    What the function range()does is create a range of numbers. At the beginning of the loop it would be a range of [2, 5). As you point out, i + 3what it is giving you is the number of columns, because if you put a four, you would have 4 columns, since the range of numbers would be in the first case [2,6). And always on the loose, the range function would return four numbers.

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