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I am studying this snippet of python code. What does X = X[:, 1] mean in last line?
def linreg(X,Y): # Running the linear regression X = sm.add_constant(X) model = regression.linear_model.OLS(Y, X).fit() a = model.params[0] b = model.params[1] X = X[:, 1] 
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In Python, [::-1] means reversing a string, list, or any iterable with an ordering. For example: hello = "Hello world"
Python also allows you to index from the end of the list using a negative number, where [-1] returns the last element. This is super-useful since it means you don't have to programmatically find out the length of the iterable in order to work with elements at the end of it.
Simply A[1:] means access elements from 1st position (don't consider A[0]).
[ : , 0 ] means (more or less) [ first_row:last_row , column_0 ] . If you have a 2-dimensional list/matrix/array, this notation will give you all the values in column 0 (from all rows). Follow this answer to receive notifications. edited Jun 11, 2019 at 0:40. NellieK.
x = np.random.rand(3,2) x Out[37]: array([[ 0.03196827, 0.50048646], [ 0.85928802, 0.50081615], [ 0.11140678, 0.88828011]]) x = x[:,1] x Out[39]: array([ 0.50048646, 0.50081615, 0.88828011]) So what that line did is sliced the array, taking all rows (:) but keeping the second column (1)
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