Meaning of X = X[:, 1] in Python

Question

I am studying this snippet of python code. What does X = X[:, 1] mean in the 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]

Asked By: Taewan

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Source

Answer 1

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)

Answered By: Leb

Answer 2

It is like you are specifying the axis. Consider the starting column as 0 then as you go through 1,2 and so on.

The syntax is x[row_index,column_index]

You can also specify a range of row values as per your need in row_index, eg:1:13 extracts first 13 rows along with whatever specified in the column

Answered By: S L SREEJITH

Answer 3

Something you should know

The term you need to search for is "slice".
x[start:end:step] is the full form.
Here we can omit some values and it will use a default value:

start defaults to 0,
end defaults to the length of the list,
and step defaults to 1.

And hence x[:] means the same as x[0:len(x):1]

Answered By: Adiraamruta

Answer 4

x[:,1] this is 2d slicing, here x[row_index, column_index]

Answered By: Ramahanisha Gunda

Answer 5

Meaning of X = X[:, 1] in Python is:

X is a dataset or a array
Say Here X have n rows and n columns
so by doing x=x[:,1] we get all the rows in x present at index 1.

for example:

x = array([[0.69859393, 0.1042432 ],
   [0.55138493, 0.18639614],
   [0.27338772, 0.80351282]])

x[:,1] = array([0.1042432 , 0.18639614, 0.80351282])

Answered By: Ramahanisha Gunda

Meaning of X = X[:, 1] in Python

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Something you should know