NumPy array basics
np.array([1,2,3])
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Creates a 1D array with values 1, 2, 3. (shape 1x3) |
np.array([(1,2,3), (4,5,6)])
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Creates 2D array of shape 2x3 with values 1,2,3,4,5,6 |
np.array([[(1,2,3), (4,5,6)], [(7,8,9), (10,11,12)]])
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Creates a 3D array with shape 2x2x3 |
np.zeros(3,4)
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Creates a 3x4 array of zeros |
np.arrange(1,60,5)
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Creates a 1D array of values 1 through 60 at steps of 5 |
a.reshape(2,3,4)
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Reshapes array a into an array of shape 2x3x4 |
a.shape
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To get the shape of the array a |
Subsetting
a[0]
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Gets the 0th element in 1D array a |
b[0,0]
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Gets the 0th element in 2D array b |
c[0,0,0]
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Gets the 0th element in 3D array c |
c[9,0,0]
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Gets the element which is the 0th element in the 0th row in the 9th depth |
Slicing arrays
1D arrays |
a[:]
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Selects everything |
a[2:5]
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Selects the 2nd through the 4th rows (does not include the 5th row) |
2D arrays |
b[:,:]
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Selects all rows and all columns |
b[:,0]
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Selects all rows, and the zeroth column |
b[0,:]
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Selects the zeroth row, and all columns in that row |
b[0:2,:]
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Selects the zeroth and first row, but NOT the second. It includes all the columns in that row |
b[0:2,0:2]
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Selects the zeroth and first row, and the zeroth and first column |
3D arrays |
c[:,:,:]
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Selects all rows and columns on all depths |
c[0,:,:]
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Selects the everything in the first depth |
c[:,0,:]
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Selects the first row of each depth |
c[:,:,0]
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Selects the first column of each depth |
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