This is a design feature of data.table objects, which don't conform to the
normal functional programming paradigm that R is usually designed to adhere to
and which Reduce expects. Specifically, they normally modify in-place rather
than leaving the original object alone.
In short, don't do that. Read more about how data.tables work. Their benefits
come with distinct disadvantages that you need to be very clear about or you
will get into trouble like this regularly.
--
Sent from my phone. Please excuse my brevity.
On May 25, 2016 8:37:10 AM PDT, James Hirschorn <james.hirsch...@hotmail.com>
wrote:
>Reduce is failing when applied to a list of elements of class
>data.table. Perhaps this is a bug?
>
>Example:
>
>library(data.table)
>
>dt1 <- data.table(x = 1:3, y = 4:6)
>dt2 <- data.table(x = 4:6, y = 1:3)
>dt3 <- data.table(x = 0:-2, y = 0:-2)
>
># This works fine
>dt1 + dt2 + dt2
># x y
># 1: 5 5
># 2: 6 6
># 3: 7 7
>
># But:
>dt_list <- list(dt1, dt2, dt3)
>Reduce("+", dt_list)
># Error in f(init, x[[i]]) : non-numeric argument to binary operator
># In addition: Warning message:
># In Reduce("+", dt_list) :
># Incompatible methods ("Ops.data.frame", "Ops.data.table") for "+"
>
>If I use data.frame instead of data.table, Reduce works properly.
>
>______________________________________________
>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.
[[alternative HTML version deleted]]
______________________________________________
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.
