tibor@kiss m@iii@g oii rub@de
2022-Sep-19 10:10 UTC
[R] Question concerning side effects of treating invalid factor levels
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
Eric Berger
2022-Sep-19 11:31 UTC
[R] Question concerning side effects of treating invalid factor levels
You are misinterpreting what is going on. The rbind command includes c(char, char, int) which produces a character vector of length 3. This is what you are rbind-ing which changes the type of the RT column. If you do rbind(df, data.frame(P="in", ANSWER="V>N", RT=round(runif(1,7000,16000),0))) you will see that everything is fine. (New factor values are created.) HTH, Eric On Mon, Sep 19, 2022 at 2:14 PM Tibor Kiss via R-help <r-help at r-project.org> wrote:> > 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 at 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.
Ebert,Timothy Aaron
2022-Sep-19 11:59 UTC
[R] Question concerning side effects of treating invalid factor levels
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-bounces at r-project.org> On Behalf Of Tibor Kiss via
R-help
Sent: Monday, September 19, 2022 6:11 AM
To: r-help at 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
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and provide commented, minimal, self-contained, reproducible code.