On Thu, 11 May 2006, Arnab mukherji wrote:
> Hi R-users,
>
> I had a minor issue while demonstating R that I can't explain. I am
> hoping someone will have suggestions. The only difference is a call to
> fix() in between that I made to ensure people were following me.
> However, that seems to have altered the way R code got executed.
>
> I was wondeirng if people have any insights.
You did not create a factor, and in the first version 'pass' is
character.
edit.data.frame (as used by fix) did some coercion.
It would be better to do
dat$pass <- factor(rep("Fail", 10), levels=c("Fail",
"Pass"))
dat[ ind, "pass"] <- "Fail"
dat[ !ind, "pass"] <- "Pass"
and also rather than fix(dat), do
invisible(edit(dat))
which does not save changes.
>
> Arnab
>
>
>
> # When it does work
> x <-letters[1:10]
> marks <-runif(10)*100
> dat <- data.frame(Student.id = x, Grade = rep(1:5,2), Marks = marks)
> ind <- dat$Marks < 50
> dat[ ind, "pass"] <- "Fail"
> dat[!ind, "pass"] <- "Pass"
> dat
> Student.id Grade Marks pass
> 1 a 1 81.91246 Fail
> 2 b 2 67.66341 Pass
> 3 c 3 4.05249 Pass
> 4 d 4 94.37248 Fail
> 5 e 5 50.83555 Pass
> 6 f 1 16.34850 Fail
> 7 g 2 43.68585 Pass
> 8 h 3 49.67190 Fail
> 9 i 4 74.41275 Fail
> 10 j 5 86.15475 Fail
>
>
>
> # When it Doesn??t Work
>
>> x <-letters[1:10]
>> marks <-runif(10)*100
>> dat <- data.frame(Student.id = x, Grade = rep(1:5,2), Marks =
marks)
>> ind <- dat$Marks < 50
>> dat[ ind, "pass"] <- "Fail"
>>
>> fix(dat)
>> dat[!ind, "pass"] <- "Pass"
> Warning message:
> invalid factor level, NAs generated in: "[<-.factor"(`*tmp*`,
iseq, value = c("Pass", "Pass", "Pass",
>
>> dat
> Student.id Grade Marks pass
> 1 a 1 72.14612 <NA>
> 2 b 2 64.34044 <NA>
> 3 c 3 20.27918 Fail
> 4 d 4 39.01875 Fail
> 5 e 5 92.19682 <NA>
> 6 f 1 58.74779 <NA>
> 7 g 2 35.31430 Fail
> 8 h 3 18.64664 Fail
> 9 i 4 51.58880 <NA>
> 10 j 5 77.94396 <NA
--
Brian D. Ripley, ripley at stats.ox.ac.uk
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595