You would be better served to reference SQL semantics (relational identity) than Network database semantics (object identifiers) for understanding data frames. The row in `aCard` is not the same as the row in `deck`, and you should not construct your algorithms based on individual rows but rather as sets of rows.
On January 3, 2019 9:15:41 AM PST, Benoit Galarneau <benoit.galarn...@polymtl.ca> wrote: >You are correct, the anti_join is working fine. >However, I still find it strange there is no "quick" way to find the >index of an item extracted from the data frame. > >This works as it returns the deck without the card no 10. >aCard = deck[10,] >cardNo = which(deck$value == aCard$value & deck$suit == aCard$suit) >deck[-cardNo,] > >But I'm still puzzled by the complexity of finding back the index of >the card with the long statement. > >Another approach that "works" is the following, but I still find it >strange to depend on data frame row names to find the index: >cardNo <- as.numeric(row.names(aCard)) > >Apologies if the above question are strange. I'm coming C++ world with > >some bias with objects. Again, since "aCard" is extracted from the >data frame, I assume (bias?) there would be a simple way to find back >the item in the data frame it came frame. Some kind of indexOf() or >similar on the container and item. > >Benoit > >Ista Zahn <istaz...@gmail.com> a écrit : > >> Hi Benoit, >> >> You can select rows from deck matched in aCard using >> >> merge(deck, aCard) >> >> Selecting rows that don't match is bit more difficult. You could do >> something like >> >> isin <- apply(mapply(function(x, y) x %in% y, deck, topCard), >> 1, >> all) >> deck[!isin, ] >> >> perhaps. >> >> Alternatively, you can use anti_join from the dplyr package: >> >> library(dplyr) >> anti_join(deck, topCard) >> >> Best, >> Ista >> >> On Thu, Jan 3, 2019 at 10:38 AM Benoit Galarneau >> <benoit.galarn...@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@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. > >______________________________________________ >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. -- Sent from my phone. Please excuse my brevity. ______________________________________________ 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.
