In your example code, the variable remains a class factor, and all entries are
valid. The variables will behave as expected given the factor levels in the
original dataframe.
(At least on my system R 4.2, in RStudio, in Windows) R returns a couple of
error messages warning me that I was bad.
What you get is NA for "not available", or "not appropriate" or a missing
value. You gave the system an invalid factor level so it was entered as
missing. If you get data that has a new factor level, you need to tell R to
expect a new factor level first.
levels(f1) <- c(levels(f1),"New Level")
levels(f1) <- c(levels(f1),c("NL1","NL2"))
Tim
-----Original Message-----
From: R-help <r-help-boun...@r-project.org> On Behalf Of Tibor Kiss via R-help
Sent: Monday, September 19, 2022 6:11 AM
To: r-help@r-project.org
Subject: [R] Question concerning side effects of treating invalid factor levels
[External Email]
Dear List members,
I have tried now for several times to find out about a side effect of treating
invalid factor levels, but did not find an answer. Various answers on
stackexchange etc. produce the stuff that irritates me without even mentioning
it.
So I am asking the list (apologies if this has been treated in the past).
If you add an invalid factor level to a column in a data frame, this has the
side effect of turning a numerical column into a column with character strings.
Here is a simple example:
> df <- data.frame(
P = factor(c("mittels", "mit", "mittels", "ueber", "mit", "mit")),
ANSWER = factor(c(rep("PP>OBJ", 4), rep("OBJ>PP", 2))),
RT = round(runif(6, 7000, 16000), 0))
> str(df)
'data.frame': 6 obs. of 3 variables:
$ P : Factor w/ 3 levels "mit","mittels",..: 2 1 2 3 1 1
$ ANSWER: Factor w/ 2 levels "OBJ>PP","PP>OBJ": 2 2 2 2 1 1
$ RT : num 11157 13719 14388 14527 14686 ..
> df <- rbind(df, c("in", "V>N", round(runif(1, 7000, 16000), 0)))
> str(df)
'data.frame': 7 obs. of 3 variables:
$ P : Factor w/ 3 levels "mit","mittels",..: 2 1 2 3 1 1 NA
$ ANSWER: Factor w/ 2 levels "OBJ>PP","PP>OBJ": 2 2 2 2 1 1 NA
$ RT : chr "11478" "15819" "8305" "8852" ...
You see that RT has changed from _num_ to _chr_ as a side effect of adding the
invalid factor level as NA. I would appreciate understanding what the purpose
of the type coercion is.
Thanks in advance
Tibor
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://nam10.safelinks.protection.outlook.com/?url=https%3A%2F%2Fstat.ethz.ch%2Fmailman%2Flistinfo%2Fr-help&data=05%7C01%7Ctebert%40ufl.edu%7C6ee1a1f50c14442beef508da9a301bde%7C0d4da0f84a314d76ace60a62331e1b84%7C0%7C0%7C637991828670135028%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=sNDYEJKhjSu%2FtrTIwZx5yVemKgDheQYXLrcQqJ2mOgo%3D&reserved=0
PLEASE do read the posting guide
https://nam10.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.r-project.org%2Fposting-guide.html&data=05%7C01%7Ctebert%40ufl.edu%7C6ee1a1f50c14442beef508da9a301bde%7C0d4da0f84a314d76ace60a62331e1b84%7C0%7C0%7C637991828670135028%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=AP%2B4fa5pvbGr3IfwdiQvjXwkOdY90CIWIWWWmpIHH7w%3D&reserved=0
and provide commented, minimal, self-contained, reproducible code.
______________________________________________
R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
