[R] how to combine logic test on vectors in R?

[Bert Gunter]

I haven't followed this thread closely, but to your question I think
maybe this is what you want"

> z <- c("","")
> all(z == "")
[1] TRUE
> z <- c("a","")
> all(z == "")
[1] FALSE

If this isn't it, just ignore without reply.

Bert Gunter

"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )

On Thu, Sep 30, 2021 at 8:51 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
>
> Yes, but the && should work within `unique(df_b$q) == ""` because the
> test should be: (IF THE DATAFRAME HAS ZERO ROW) OR (ALL THE ELEMENTS
> OF $q ARE EMPTY) THEN (PRINT empty).
> Can I collapse the TRUE FALSE of `unique(df_b$q) == ""`into a single FALSE?
>
> On Thu, Sep 30, 2021 at 4:28 PM Sarah Goslee <sarah.goslee using gmail.com> wrote:
> >
> > Hi,
> >
> > The OR operator you used is working as expected: || starts from the
> > left and evaluates only enough of the options to determine the
> > results. The first test is TRUE,  so the result is TRUE. It sounds
> > like you might actually want an AND operator, & or &&, which will only
> > return TRUE if all elements are TRUE,
> >
> > More on logical operators:
> > https://stat.ethz.ch/R-manual/R-devel/library/base/html/Logic.html
> >
> > Sarah
> >
> > On Thu, Sep 30, 2021 at 9:07 AM Luigi Marongiu <marongiu.luigi using gmail.com> wrote:
> > >
> > > Hello,
> > > I have two data frames, each with three rows:
> > > ```
> > > df_a <- data.frame(a = letters[1:3], b = LETTERS[1:3], q = c("", "", ""),
> > > stringsAsFactors = FALSE)
> > > df_b <- data.frame(a = letters[4:6], b = LETTERS[4:6], q = c("", "", "1.5"),
> > > stringsAsFactors = FALSE)
> > > ```
> > > I need to test whether the dataframe has been selected and if there is
> > > a value in the q column. I combined in the following test:
> > > ```
> > > if (nrow(df_a) == 0 || unique(df_a$q) == "") {
> > > print("empty")
> > > }
> > > if (nrow(df_b) == 0 || unique(df_b$q) == "") {
> > > print("empty")
> > > }
> > > ```
> > > The test for df_a worked as expected:
> > > ```
> > > > nrow(df_a) == 0
> > > [1] FALSE
> > > > unique(df_a$q) == ""
> > > [1] TRUE
> > > > (nrow(df_a) == 0 || unique(df_a$q) == "")
> > > [1] TRUE
> > > > if (nrow(df_a) == 0 || unique(df_a$q) == "") {
> > > + print("empty")
> > > + }
> > > [1] "empty"
> > > ```
> > > but the one for df_b did not:
> > > ```
> > > > nrow(df_b) == 0
> > > [1] FALSE
> > > > unique(df_b$q) == ""
> > > [1]  TRUE FALSE
> > > > (nrow(df_b) == 0 || unique(df_b$q) == "")
> > > [1] TRUE
> > > > unique(df_b$q)
> > > [1] ""    "1.5"
> > > ```
> > > I say that it did not work because unique(df_b$q) IS NOT "", hence
> > > `(nrow(df_b) == 0 || unique(df_b$q) == "")` should be FALSE, instead R
> > > evaluated the first element of unique(df_b$q) == "", which is TRUE.
> > > How can I properly implement a logic test on vectors?
> > >  Thank you
> > >
> > > ______________________________________________
> > > R-help using 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.
> >
> >
> >
> > --
> > Sarah Goslee (she/her)
> > http://www.sarahgoslee.com
>
>
>
> --
> Best regards,
> Luigi
>
> ______________________________________________
> R-help using 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.