... Perhaps worth noting is that the row indices can be created
directly without row():
result[cbind(rep.int(seq_len(6),5), as.vector(x))] <- 1
but the downside is that you have to know that a matrix is a vector
"stored" in column major order. I find this arcane detail quite handy,
though.
Cheers,
Bert
Bert Gunter
"The trouble with having an open mind is that people keep coming along
and sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )
On Tue, Dec 22, 2015 at 3:03 PM, Marc Schwartz <marc_schwa...@me.com> wrote:
>
>> On Dec 22, 2015, at 4:42 PM, Dimitri Liakhovitski
>> <dimitri.liakhovit...@gmail.com> wrote:
>>
>> # I have a matrix x:
>>
>> k <- 20
>> N <- 5
>> set.seed(123)
>> x <- matrix(c(sample(1:k, N, replace = F),
>> sample(1:k, N, replace = F),
>> sample(1:k, N, replace = F),
>> sample(1:k, N, replace = F),
>> sample(1:k, N, replace = F),
>> sample(1:k, N, replace = F)), byrow = T, ncol = 5)
>> colnames(x) <- paste0("column", 1:5)
>> (x)
>>
>> # I want to reshape it into a matrix 'result' with k columns (not N).
>> # 'result' should contain the same number of rows as x, and it should have
>> # in each row 1s in those columns that correspond to the entries in x
>> in the same row.
>> # For example, the first row of 'result' should contain 1s in columns
>> 6, 8, 15, 16, and 17, etc.
>> # The remaining entries should be zeros.
>>
>> result <- matrix(rep(0, nrow(x) * k), nrow = nrow(x))
>> colnames(result) <- paste0("item", 1:k)
>>
>> # I can see how to do it by looping through rows of result.
>> # But I need to do it fast (not using a loop).
>> # I feel like I should subset 'result' with 'x', but I am not sure how.
>>
>> Thank you very much!
>
>
> Something like this might work for you:
>
> result <- matrix(0, nrow(x), k)
>
>
>> result
> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
> [1,] 0 0 0 0 0 0 0 0 0 0 0 0
> [2,] 0 0 0 0 0 0 0 0 0 0 0 0
> [3,] 0 0 0 0 0 0 0 0 0 0 0 0
> [4,] 0 0 0 0 0 0 0 0 0 0 0 0
> [5,] 0 0 0 0 0 0 0 0 0 0 0 0
> [6,] 0 0 0 0 0 0 0 0 0 0 0 0
> [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
> [1,] 0 0 0 0 0 0 0 0
> [2,] 0 0 0 0 0 0 0 0
> [3,] 0 0 0 0 0 0 0 0
> [4,] 0 0 0 0 0 0 0 0
> [5,] 0 0 0 0 0 0 0 0
> [6,] 0 0 0 0 0 0 0 0
>
>
> result[cbind(as.vector(row(x)), as.vector(x))] <- 1
>
>
>> result
> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12]
> [1,] 0 0 0 0 0 1 0 1 0 0 0 0
> [2,] 1 0 0 0 0 0 0 1 0 1 1 0
> [3,] 0 1 0 0 0 0 0 0 1 1 0 0
> [4,] 1 0 0 0 1 1 0 0 0 0 0 0
> [5,] 0 0 0 0 0 0 0 0 0 0 1 1
> [6,] 0 0 1 0 1 0 0 0 0 0 1 0
> [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
> [1,] 0 0 1 1 1 0 0 0
> [2,] 0 0 0 0 1 0 0 0
> [3,] 1 0 0 0 0 0 0 1
> [4,] 0 0 0 1 0 1 0 0
> [5,] 0 1 0 0 1 1 0 0
> [6,] 0 0 1 0 0 0 1 0
>
>
> See ?row
>
> Regards,
>
> Marc Schwartz
>
> ______________________________________________
> 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.
______________________________________________
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.
