# FAQ: Linear Regression - Scikit-Learn

This community-built FAQ covers the “Scikit-Learn” exercise from the lesson “Linear Regression”.

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There are so many modes and data_types which are to learn in CodeAcademy. Are there a comparative table of all the models, which could help us to sellect the right method on the approptiate data. E.g. with columns:

`method/model | method_description | code_example | numeric/categorical data | min/max quantity of variables | advantages/disadvantages | alternative method`

What does .reshape do in Linear Regression https://www.codecademy.com/paths/machine-learning/tracks/regression-skill-path/modules/linear-regression-skill-path/lessons/linear-regression/exercises/sklearn. This has not been explained as far as I can see

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`temperature.reshape(-1, 1)` returns a 2D array which is the transposed `temperature`.

``````temperature = np.array(range(60, 100, 2))
print(temperature)
# [60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98]

temperature = temperature.reshape(-1, 1)
print(temperature)
'''
[[60]
[62]
[64]
[66]
[68]
[70]
[72]
[74]
[76]
[78]
[80]
[82]
[84]
[86]
[88]
[90]
[92]
[94]
[96]
[98]]
'''
``````

The reason why we need to do this is because the `.fit()` and `.predict()` methods expect a 2D array. I agree with you that there’s not enough explanation on this point.

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I understand (-1, 1), the 1 means the number of column, but how about the -1? the minus row?

2 Likes

When reshaping an array, the returned array must have the same number of elements as the original array. By using `-1`, even if you don’t know the number of elements in the original array, you can make the returned array to have the same number of elements. (Only one shape dimension can be `-1`.) For example, if the original array has `n` elements, `.reshape(-1, 1)` is equivalent to `.reshape(n, 1)`.

2 Likes

Using Skikit-learn’s linear regression model, I tried plotting the line I got using list comprehension

``````y_predictions = [element * m + b for element in X]
``````

Then I got this error which seems like I need to encapsulate each point in its own array? How do I go about doing that? I imagine it has to do with getting the predicted sales without using list comprehension.

image|690x386

I needed to use the .predict function

why we did not .reshape(-1,1) both in y = sales???thanks for your answer:)

why we did not .reshape(-1,1) both in y = sales???thanks for your answer:)!!!

`.fit()` method of `LinearRegression()` takes two arguments `X` and `y`, and a 2D array is expected for `X`. `y` does not have to be a 2D array.

1 Like