[R] question about "lines"

[Duncan Murdoch]

On 13-09-17 6:36 PM, meng wrote:
> Thanks for your reply.
>
> Is "fitted(lm(...))" the same as "values" of lines(values)?
>
> If yes,then why the range of lines(values) is different from
> range(fitted(lm(...)))?

You are plotting against the wrong x axis, and you don't see all the values.

Duncan Murdoch

> If no, what "values" refers to?
>
>
>
> At 2013-09-17 20:56:04,"Duncan Murdoch" <murdoch.duncan at gmail.com> wrote:
>>On 13-09-17 8:06 AM, meng wrote:
>>> Hi all:
>>> I met a question about "lines".
>>>
>>>
>>> attach(cars)
>>>
>>>
>>> plot(dist ~ speed)
>>> #add the regression line to the plot
>>> lines(fitted(lm(dist~speed)) ~ speed)
>>>
>>>
>>> plot(dist ~ speed)
>>> #what kind of curve does the following command add to the plot?
>>> lines(fitted(lm(dist~speed)))
>>>
>>>
>>> My question is :
>>> what kind of curve does the last command add to the plot?
>>
>>Look at the class of fitted(lm(...)).  It is "numeric".  So what you're
>>seeing is the same as if you computed the fitted values, and then did
>>
>>lines(values)
>>
>>Since values is just a vector of numbers, that will plot them as y
>>values against x values 1:length(values).  That's unlikely to be a
>>useful thing to do.
>>
>>Duncan Murdoch
>>
>>>
>>>
>>> My guess:maybe the level of fitted values?
>>>> range(fitted(lm(dist~speed)))
>>> [1] -1.84946 80.73112
>>>
>>>
>>> But from the plot,I can see the range of the curve is about 10 to 40 more or less,which is different from(-1.84946, 80.73112).So the curve must not be the fitted values.What kind of curve does the last command add to the plot then?
>>>
>>>
>>>
>>>
>>> Many thanks for your help
>>>
>>>
>>> My best
>>> 	[[alternative HTML version deleted]]
>>>
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>>>
>>
>
>
>