[R] How to invert a list ?

[Carlos Petti]

Do not worry, I found the solution.

I had a list, as follows :

x <- list()
x$i <- 5
x$j <- 9
x$k <- 15
names(x$i) <- "a"
names(x$j) <- "b"
names(x$k) <- "b"

And I wanted to obtain a list, as follows :
$a
i
5

$b
 j  k
 9 15

My solution :

n <- sapply(x, names)
m <- sapply(x, c, use.names = FALSE)
tapply(m, n, c)

Thanks for answers.
Carlos

2010/8/11 Wu Gong <wg2f at mtmail.mtsu.edu>:
> Hi Carlos,
>
> I don't know what kind of data you really have. It's would be helpful if you give a sample data. You really don't need to use sapply.
>
> R can assign names through vectors:
>
> names(y) <- names(x)
>
> Or:
>
> names(y) <- c("NameA","NameB")
>
> Regards,
>
> Wu
>
>
>
> ________________________________________
> From: Carlos Petti [carlos.petti at gmail.com]
> Sent: Wednesday, August 11, 2010 5:39 AM
> To: Wu Gong
> Cc: r-help at r-project.org
> Subject: Re: [R] How to invert a list ?
>
> Or rather :
> n <- sapply(x, function(i) names(i))
> tapply(x, n, names)
>
> 2010/8/11 Carlos Petti <carlos.petti at gmail.com>:
>> A beginning of solution...
>>
>> n <- sapply(x, function(i) names(i))
>> tapply(x, n, c)
>>
>> 2010/8/11 Carlos Petti <carlos.petti at gmail.com>:
>>> Thanks.
>>>
>>> On the other hand,
>>> I try to obtain the same result but from this list :
>>>
>>> x <- list()
>>> x$i <- 5
>>> x$j <- 9
>>> x$k <- 15
>>> names(x$i) <- "a"
>>> names(x$j) <- "b"
>>> names(x$k) <- "b"
>>>
>>> Thanks in advance,
>>> Carlos
>>>
>>> 2010/8/10 Wu Gong <wg2f at mtmail.mtsu.edu>:
>>>>
>>>> Hi Carlos,
>>>>
>>>> I give a handmade code, hope it helps.
>>>>
>>>> y <- list()
>>>> y$a <- a
>>>> y$b <- c(b,c)
>>>> names(y$a) <- "i"
>>>> names(y$b) <- c("j","k")
>>>>
>>>>
>>>> Carlos Petti wrote:
>>>>>
>>>>> a <- 5
>>>>> names(a) <- "a"
>>>>> b <- 9
>>>>> names(b) <- "b"
>>>>> c <- 15
>>>>> names(c) <- "c"
>>>>> x <- list("i" = a, "j" = b, "j" = c)
>>>>>
>>>>
>>>>
>>>> -----
>>>> A R learner.
>>>> --
>>>> View this message in context: http://r.789695.n4.nabble.com/How-to-invert-a-list-tp2320108p2320433.html
>>>> Sent from the R help mailing list archive at Nabble.com.
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> 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.
>>>>
>>>
>>
>