[R] Least Squares Fit

[Martin Maechler]

>>>>> "Jon" == Jonathan Baron <baron at psych.upenn.edu>
>>>>>     on Sun, 2 May 2004 07:10:10 -0400 writes:

    Jon> On 05/02/04 03:26, Fred J. wrote:
    >> Hello
    >> 
    >> I need to plot the least squares fit and get the slope of
    >> the line that best fit the data. after reading lm and
    >> lsfit, since not being able to understand the use of the
    >> second argument "y" for the lsfit, I am giving the lm a
    >> go, but know not why the code below does not draw the
    >> line on the plot. e.g. well.. why -50 Intercept?  thanks
    >> 
    >> x <- 1:10; y <- x+50
    >> plot(x,y)
    >> z <- lm(as.data.frame(cbind(x,y))))
    >> abline(z)
    >> 
    >>> z$coefficients
    >> (Intercept)           y
    >> -50           1

Did you, "Fred J.",  really ever take time to read the
"Introduction to R", maybe with a pencil in your hand to mark a
few things?


    Jon> The lm() is predicting x from y, and plot() is plotting
    Jon> y as a function of x.

    Jon> Try 
    Jon> plot(x,y) 
    Jon> abline(lm(y~x))

or in this case, the more intuitive

     plot(y ~ x)
abline(lm(y ~ x))

y ~ x  : `` y is modeled by (predictor) x ''

--
Martin