AFAIK the intent of the designers of the data frame class was that rownames be unique and be useful for tracking the origins of records in data subsets. However, after a few merging operations the traceability becomes murky anyway and relational set theory avoids them. Neither data.table nor dplyr packages support them. In short, base R data import functions will create rownames on data frames so you should be able to depend on it as long as you stick with base R.
On January 3, 2019 9:39:44 AM PST, Benoit Galarneau <benoit.galarn...@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 <jdnew...@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.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. >> >> -- >> Sent from my phone. Please excuse my brevity. -- 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.
