案例学习：预测房价

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From the course by 华盛顿大学

机器学习：回归

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案例学习：预测房价

From the lesson

Simple Linear Regression

Our course starts from the most basic regression model: Just fitting a line to data. This simple model for forming predictions from a single, univariate feature of the data is appropriately called "simple linear regression".<p> In this module, we describe the high-level regression task and then specialize these concepts to the simple linear regression case. You will learn how to formulate a simple regression model and fit the model to data using both a closed-form solution as well as an iterative optimization algorithm called gradient descent. Based on this fitted function, you will interpret the estimated model parameters and form predictions. You will also analyze the sensitivity of your fit to outlying observations.<p> You will examine all of these concepts in the context of a case study of predicting house prices from the square feet of the house.

- Emily FoxAmazon Professor of Machine Learning

Statistics - Carlos GuestrinAmazon Professor of Machine Learning

Computer Science and Engineering

[MUSIC]

Okay so in the first course of this specialization,

we introduced this block diagram or flow chart for regression.

As well as a bunch of other machine learning tasks, but

I just want to walk through this again.

So we're going to assume that we have some training data.

Okay, so all of a sudden I've said the word training data,

and I hadn't said that to this point.

That's a topic we discussed at a very high level

in the first course of the specialization,

and we're gonna discuss the concepts of training data, test data, validation sets,

lots of other ideas about fitting our models and accessing our fits.

And chosing between models and all these different topics.

We're gonna discuss that in this course.

But for right now, if you don't know what it means to have training data, go back to

the first course of this specialization, watch that video or look it up online.

For now, I'm gonna assume that you know that we've some training data and

we're using our training data to fit a specific model.

And for the rest of this module, that's gonna suffice,

we're only looking at training data.

And all the other discussion about validation sets, test sets,

and everything like this, choosing between models,

assessing the fit of the models, that's going to come later in this course.

Okay, so when I talk about data in the rest of this module,

I'm assuming we're talking about just our training set,

that we've already done some split and we have our training data, okay.

Think I've said enough on that.

So, we have our training data and in this case,

that's gonna be some table of house id,

house square feet and then the house sales price.

And we have this big table of all these quantities.

And then what we're going to do, is extract some features.

So maybe, actually, at this point instead of specifically saying how square feet,

I can just say that there's some set of house attributes.

We might have things in addition to square feet.

And so one step we're gonna have to do is figure out what input we're gonna use for

our regression model.

We're gonna talk about more general features later in the course, but for

now we're just assuming a simple setup where we're gonna choose one of our house

attributes, call that the input to this regression model, and work from there.

So, we've talked about using square feet as our selected input

and then we're gonna use our Machine Learning model,

which is regression, to predict our house sales prices.

So y hat represents our predicted,

house sales price.

And how are we predicting it?

Well, based on some estimated line or curve,

so this is our, f hat is our estimated function.

That's fit from our data set, or, specifically our training data set.

And how are we gonna determine f hat?

Or how are we gonna estimate this function?

Well, first we're gonna need to describe some quality metric that says

I should describe what Y is.

I already mentioned this earlier, but let's write it down explicitly.

This is the sales price, the actual

sales price of our houses, and we're gonna compare the actual

sales price to the predicted sales price using the any given F hat.

We're gonna say how well did we do?

And that's what the quality metric is.

So there's gonna be some error in our predicted values.

And the machine learning algorithm we're gonna use to fit these

regression models is gonna try to minimize that error.

So it's gonna search over all these functions to reduce the error

in these predicted values.

Okay, so this is our overall flow chart and

we're gonna walk through the various components of this throughout this

module and in more depth in the rest of this course.

[MUSIC]

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