You have an object named "ozone" kicking around in your workspace/global
environment. This is apparently not of mode "numeric" and it is masking
the "ozone" object (column) from the attached data frame "test".
Simply doing ls() would have told you this.
Presumably you also got a warning about this when you attached test.
Heed the warning!
As others have advised you ***don't use attach()***!!!
Instead, use "data= ..." in your call to lm().
cheers,
Rolf Turner
On 20/10/12 10:26, Michael Grant wrote:
New installation seems to have behavior I cannot figure out. Here is
illustrative sequence where I load a small data set (test) from Crawley's files
and try to run a simple linear model and get an error message. Oddly, R
reports that the variable 'test$ozone' is numeric while, after attaching test,
the variable ozone is not numeric. Can someone please help? This behavior is
occurring with multiple data sets loaded from outside R. Thank you in advance.
Michael Grant
Example:
test
ozone garden
1 3 A
2 5 B
3 4 A
4 5 B
5 4 A
6 6 B
7 3 A
8 7 B
9 2 A
10 4 B
11 3 A
12 4 B
13 1 A
14 3 B
15 3 A
16 5 B
17 5 A
18 6 B
19 2 A
20 5 B
is.data.frame(test)
[1] TRUE
is.numeric(test$ozone)
[1] TRUE
is.factor(test$garden)
[1] TRUE
lm(ozone~garden)
Error in model.frame.default(formula = ozone ~ garden, drop.unused.levels =
TRUE) :
invalid type (list) for variable 'ozone'
attach(test)
is.numeric(ozone)
[1] FALSE
is.numeric(test$ozone)
[1] TRUE
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