slice() fails on tbl_sqlite

[vjcitn]

if an intrinsic limitation man page should clarify

> mtcars %>% slice(1:4)
   mpg cyl disp  hp drat    wt  qsec vs am gear carb
1 21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
2 21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
3 22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
4 21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
> con = dbConnect(dbDriver("SQLite"), "/tmp/cars2.sqlite")
> dbWriteTable(con, "carsdb", mtcars)
[1] TRUE
> src_sqlite("/tmp/cars2.sqlite") %>% tbl("carsdb") %>% slice(1:4)
Error in UseMethod("slice_") : 
  no applicable method for 'slice_' applied to an object of class "c('tbl_sqlite', 'tbl_sql', 'tbl')"

Enter a frame number, or 0 to exit   

1: src_sqlite("/tmp/cars2.sqlite") %>% tbl("carsdb") %>% slice(1:4)
2: withVisible(eval(e, env))
3: eval(e, env)
4: eval(expr, envir, enclos)
5: slice(`src_sqlite("/tmp/cars2.sqlite") %>% tbl("carsdb")`, 1:4)
6: slice_(.data, .dots = lazyeval::lazy_dots(...))

[hadley]

Yeah, all we can do here is document it. You'll never be able to slice() a sql data source.

[vjcitn]

couldn't you set this up with an offset and a limit?

On Thu, Oct 30, 2014 at 5:22 PM, Hadley Wickham notifications@github.com
wrote:

Yeah, all we can do here is document it. You'll never be able to slice()
a sql data source.

—
Reply to this email directly or view it on GitHub
#720 (comment).

[hadley]

@vjcitn that's only one type of slice - you can also do slice(mtcars, seq(1, n(), by = 2)). If you want to do a similar transformation with sql, you could use filter() + row_number() but it's not obvious that it's a meaningful operation because rows in SQL have no intrinsic order.

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