[R] Accessing Data Frame

[Greg Snow]

Here is another approach that uses only the default packages:

> onecar <- mtcars[10,]
> w <- which(duplicated(rbind(mtcars,onecar), fromLast = TRUE))
> w
[1] 10
> mtcars.subset <- mtcars[-w,]
>
>
> threecars <- mtcars[c(1,10,15),]
> w <- which(duplicated(rbind(mtcars,threecars), fromLast=TRUE))
> w
[1]  1 10 15
> mtcars.subset <- mtcars[-w, ]

This works with a subset of 1, or more than 1, but could cause
problems if you have duplicate rows in your original data frame.

If you are willing to use a non-default package then there are many
possibilities.  The anti_join function from the dplyr package has
already been mentioned, but the setdiff function from dplyr would also
work here and would be a little simpler for your example:

> library(dplyr)
> mtcars.subset2 <- setdiff(mtcars,threecars)
> identical(as.list(mtcars.subset), as.list(mtcars.subset2))
[1] TRUE

The as.list function above was to remove some attributes that were
different between the outputs.

On Thu, Jan 3, 2019 at 10:59 AM Benoit Galarneau
<benoit.galarneau using polymtl.ca> wrote:
>
> Thanks for the feedback.
> Point taken about the data.table package, I will take a look for sure.
> As I am new to the R programming, I'm exploring with the default
> libraries as a start.
>
> I have various options that works like this one:
>
> topCard <- deck[1,]
> #Remove card from deck using row name
> deck <- deck[!rownames(deck) %in% row.names(topCard),]
>
> Is it recommended/safe/good practice to work on items using the item names?
>
> Benoit
>
> Jeff Newmiller <jdnewmil using dcn.davis.ca.us> a écrit :
>
> >> In my programmer's head, something similar to this should "work": ...
> >> deck[aCard]
> >
> > There are some people who agree with you... see the data.table
> > package, which can be made to behave like this.
> >
> > Keep in mind that the aCard data frame in general may have a
> > different set of column names or more than one row. (I would be
> > concerned that the logic of your application was inefficiently
> > designed if `deck` actually has the same columns as `aCard` as in
> > your example.) Others have pointed out that data frames are
> > typically combined using the merge function, which allows matching
> > columns to be specified very flexibly.
> >
> >
> > On January 3, 2019 6:50:22 AM PST, Benoit Galarneau
> > <benoit.galarneau using polymtl.ca> wrote:
> >> Hi everyone,
> >> I'm new to the R world.
> >> Probably a newbie question but I am stuck with some concept with data
> >> frame.
> >> I am following some examples in the "Hands-On Programming with R".
> >>
> >> In short, how can I access/filter items in a data frame using a
> >> variable.
> >>
> >> One example consists of manipulating elements from a deck of card:
> >>
> >>> deck
> >>     face     suit value
> >> 1   king   spades    13
> >> 2  queen   spades    12
> >> 3   jack   spades    11
> >> 4    ten   spades    10
> >> etc.
> >>
> >> Let's say I want to remove or filter out the first card. I know I
> >> could do deck[-1].
> >>
> >> But let's say I have: topCard <- deck[1,]
> >>
> >> topCard is then a list of 3 elements
> >>> topCard
> >>   face   suit value
> >> 1 king spades    13
> >>
> >> My question is the following, how can I remove or filter out the deck
> >> using the topCard variable.
> >>
> >> In my programmer's head, something similar to this should "work":
> >>> deck[10,]
> >>    face   suit value
> >> 10 four spades     4
> >>> aCard <- deck[10,]
> >>> aCard
> >>    face   suit value
> >> 10 four spades     4
> >>> deck[aCard]
> >> Error in `[.default`(deck, aCard) : invalid subscript type 'list'
> >>
> >> Wihout having to specify all elements in the logical tests.
> >>
> >> deck[deck$face == aCard$face & deck$suit == aCard$suit & deck$value ==
> >>
> >> aCard$value,]
> >>    face   suit value
> >> 10 four spades     4
> >>
> >> ______________________________________________
> >> 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.
> >
> > --
> > Sent from my phone. Please excuse my brevity.
>
> ______________________________________________
> 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.



-- 
Gregory (Greg) L. Snow Ph.D.
538280 using gmail.com