檢視“統計分析：使用 R 入門/R/簡單的 R 會話”的原始碼

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|Even though R has not been fully introduced yet, it is instructive to see how simple a useful R session can be. As an example, we will fit a statistical model using the cars data from the previous topic, and see how to produce a similar plot to [[:image:R-car_stopping_distances_1920+linear.svg| Figure 1.2b]], with a straight best-fit line. This is a common task in many simple analyses. 

Some of the commands in this example will be unfamiliar: don't worry, the main point is not to understand the commands, but to get an overall sense of how R works. Nevertheless, if you ''do'' want to understand the commands fully, you will need to know about [[../R/Data frames|data frames]] (essentially, tables of data with named columns) and [[../R/Model formulae|model formulae]] (essentially, a notation of the form <code>''a'' ~ ''b'' + ''c''</code>, meaning ''a'' is predicted by ''b'' and ''c'').

|plot(dist ~ speed, data{{=}}cars)                     #A common way of creating a specific plot is via a model formula
straight.line.model <- lm(dist~speed, data{{=}}cars)  #This creates and stores a model ("lm" means "Linear Model").
abline(straight.line.model, col{{=}}"red")            #"abline" will also plot a straight line from a model
straight.line.model                               #Show model predictions (estimated slope & intercept of the line)
|<nowiki>> plot(dist ~ speed, data=cars)                     #A common way of creating a specific plot is via a model formula
> straight.line.model <- lm(dist~speed, data=cars)  #This creates and stores a model ("lm" means "Linear Model").
> abline(straight.line.model, col="red")            #"abline" will also plot a straight line from a model
> straight.line.model                               #Show model predictions (estimated slope & intercept of the line)

Call:
lm(formula = dist ~ speed, data = cars)

Coefficients:
(Intercept)        speed  
    -17.579        3.932  

</nowiki>|Note that unlike the examples in the [[../R/Graphics|graphics topic]], we have plotted the data by specifying a  [[../R/Model formulae|model formula]], rather than just giving the name of the dataset. Although in this case the resulting plot is the same as seen with <code>plot(cars)</code>, the formula interface makes it clearer what is being plotted.
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