[R] Accessing Data Frame

[Jeff Newmiller]

>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
>
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-- 
Sent from my phone. Please excuse my brevity.