[R] Accessing Data Frame

[Benoit Galarneau]

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 <istazahn using 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.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
>>
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