Hi,
this is a misunderstanding of my question. I wasn’t worried about invalid
factor levels that produce NA. My question was why a column changes its class,
which I thought was a side effect. If you add a vector containing one character
string, the class of the whole vector becomes _chr_. And after this element has
been added to a column, we have two NAs for the column which are factors, and a
character string, which is responsible for the change of a numerical vector
into a character string vector (see ?c, where you find: "The output type is
determined from the highest type of the components in the hierarchy NULL < raw
< logical < integer < double < complex < character < list < expression.“).
Best
Tibor
> Am 19.09.2022 um 13:59 schrieb Ebert,Timothy Aaron <teb...@ufl.edu>:
>
> 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
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