so I'm trying to construct 2-D arrays with the numpy function arange and I'm having a bit of trouble.
I'd like to construct a 2D array of ints where the entry at position i,j is (i+j). That is, an array like this (reccommended to use arange):
[[ 0 1 2 3 4 5 6 7 8 9]
[ 1 2 3 4 5 6 7 8 9 10]
[ 2 3 4 5 6 7 8 9 10 11]
[ 3 4 5 6 7 8 9 10 11 12]
[ 4 5 6 7 8 9 10 11 12 13]
[ 5 6 7 8 9 10 11 12 13 14]
[ 6 7 8 9 10 11 12 13 14 15]
[ 7 8 9 10 11 12 13 14 15 16]
[ 8 9 10 11 12 13 14 15 16 17]
[ 9 10 11 12 13 14 15 16 17 18]]
I also need to construct another array (100x100) where the value at index i,j is True if j is a divisor of i and False otherwise. That is, an array that looks like:
[[False False False ..., False False False]
[ True True True ..., True True True]
[ True False True ..., False True False]
...,
[ True False False ..., True False False]
[ True False False ..., False True False]
[ True False False ..., False False True]]
I am not able to use nested loops (though I can use loops to construct the lists) and I cannot use the np.array function. I currently have the following that works for the first part, but I would like to have it all as one array, not several printed out.
i = 0
j= 10
for i in range(10):
lis = np.arange(i, j)
i += 1
j += 1
print(np.array(lis))
If I could get some help, that'd be great
EDIT: my current code shows this output:
[0 1 2 3 4 5 6 7 8 9]
[ 1 2 3 4 5 6 7 8 9 10]
[ 2 3 4 5 6 7 8 9 10 11]
[ 3 4 5 6 7 8 9 10 11 12]
[ 4 5 6 7 8 9 10 11 12 13]
[ 5 6 7 8 9 10 11 12 13 14]
[ 6 7 8 9 10 11 12 13 14 15]
[ 7 8 9 10 11 12 13 14 15 16]
[ 8 9 10 11 12 13 14 15 16 17]
[ 9 10 11 12 13 14 15 16 17 18]
Why would the first line not be lining up with the other rows?
To do the first one with numpy:
>>> a = np.arange(11)
>>> a[:,None]+a
array([[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10],
[ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11],
[ 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
[ 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13],
[ 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14],
[ 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15],
[ 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16],
[ 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17],
[ 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18],
[ 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19],
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20]])
For the second array, @Divakar has a good approach. Maybe a bit simpler syntax to do this:
>>> (a%a[:,None])==0
array([[ True, True, True, True, True, True, True, True, True, True, True],
[ True, True, True, True, True, True, True, True, True, True, True],
[ True, False, True, False, True, False, True, False, True, False, True],
[ True, False, False, True, False, False, True, False, False, True, False],
[ True, False, False, False, True, False, False, False, True, False, False],
[ True, False, False, False, False, True, False, False, False, False, True],
[ True, False, False, False, False, False, True, False, False, False, False],
[ True, False, False, False, False, False, False, True, False, False, False],
[ True, False, False, False, False, False, False, False, True, False, False],
[ True, False, False, False, False, False, False, False, False, True, False],
[ True, False, False, False, False, False, False, False, False, False, True]], dtype=bool)
Per your first question:
np.add(*np.indices((nrow, ncol)))
For nrow=5
, ncol=6
you get
array([[0, 1, 2, 3, 4, 5],
[1, 2, 3, 4, 5, 6],
[2, 3, 4, 5, 6, 7],
[3, 4, 5, 6, 7, 8],
[4, 5, 6, 7, 8, 9]])
This method doesn't use the numpy.arange
function, though I find it more readable. Moreover, it supports cases when nrow != ncol
.
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