[R] Accessing Data Frame

[Rui Barradas]

Hello,

Inline.

Às 14:50 de 03/01/2019, Benoit Galarneau escreveu:
> 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].

No, to filter out the first card you need a comma after the -1.

deck[-1, ]    # filter the first row out
deck[-1]      # filter the first column out

> 
> 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.

merge(topCard, deck, all.x = TRUE, all.y = FALSE)

Hope this helps,

Rui Barradas


> 
> 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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