These classes are used to define callback behaviors.
Callback interface definition, all callback functions should inherit from this class.
Callback function that is used only for side effects, no results are returned.
Callback function that combines each result together at the end.
Callback function that accumulates a single result. Requires the parameter acc to specify
the initial value of the accumulator. The parameter acc is NULL by default.
Other chunked: melt_delim_chunked,
read_delim_chunked,
read_lines_chunked
## If given a regular function it is converted to a SideEffectChunkCallback # view structure of each chunk read_lines_chunked(readr_example("mtcars.csv"), str, chunk_size = 5)#> chr [1:5] "\"mpg\",\"cyl\",\"disp\",\"hp\",\"drat\",\"wt\",\"qsec\",\"vs\",\"am\",\"gear\",\"carb\"" ... #> chr [1:5] "18.7,8,360,175,3.15,3.44,17.02,0,0,3,2" ... #> chr [1:5] "19.2,6,167.6,123,3.92,3.44,18.3,1,0,4,4" ... #> chr [1:5] "10.4,8,472,205,2.93,5.25,17.98,0,0,3,4" ... #> chr [1:5] "33.9,4,71.1,65,4.22,1.835,19.9,1,1,4,1" ... #> chr [1:5] "19.2,8,400,175,3.08,3.845,17.05,0,0,3,2" ... #> chr [1:3] "19.7,6,145,175,3.62,2.77,15.5,0,1,5,6" ...#> NULL# Print starting line of each chunk f <- function(x, pos) print(pos) read_lines_chunked(readr_example("mtcars.csv"), SideEffectChunkCallback$new(f), chunk_size = 5)#> [1] 1 #> [1] 6 #> [1] 11 #> [1] 16 #> [1] 21 #> [1] 26 #> [1] 31#> NULL# If combined results are desired you can use the DataFrameCallback # Cars with 3 gears f <- function(x, pos) subset(x, gear == 3) read_csv_chunked(readr_example("mtcars.csv"), DataFrameCallback$new(f), chunk_size = 5)#> #> #> #> #> #> #> #> #> #> #> #> #> #>#> # A tibble: 15 x 11 #> mpg cyl disp hp drat wt qsec vs am gear carb #> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> #> 1 21.4 6 258 110 3.08 3.22 19.4 1 0 3 1 #> 2 18.7 8 360 175 3.15 3.44 17.0 0 0 3 2 #> 3 18.1 6 225 105 2.76 3.46 20.2 1 0 3 1 #> 4 14.3 8 360 245 3.21 3.57 15.8 0 0 3 4 #> 5 16.4 8 276. 180 3.07 4.07 17.4 0 0 3 3 #> 6 17.3 8 276. 180 3.07 3.73 17.6 0 0 3 3 #> 7 15.2 8 276. 180 3.07 3.78 18 0 0 3 3 #> 8 10.4 8 472 205 2.93 5.25 18.0 0 0 3 4 #> 9 10.4 8 460 215 3 5.42 17.8 0 0 3 4 #> 10 14.7 8 440 230 3.23 5.34 17.4 0 0 3 4 #> 11 21.5 4 120. 97 3.7 2.46 20.0 1 0 3 1 #> 12 15.5 8 318 150 2.76 3.52 16.9 0 0 3 2 #> 13 15.2 8 304 150 3.15 3.44 17.3 0 0 3 2 #> 14 13.3 8 350 245 3.73 3.84 15.4 0 0 3 4 #> 15 19.2 8 400 175 3.08 3.84 17.0 0 0 3 2# The ListCallback can be used for more flexible output f <- function(x, pos) x$mpg[x$hp > 100] read_csv_chunked(readr_example("mtcars.csv"), ListCallback$new(f), chunk_size = 5)#> #> #> #> #> #> #> #> #> #> #> #> #> #>#> [[1]] #> [1] 21.0 21.0 21.4 18.7 #> #> [[2]] #> [1] 18.1 14.3 19.2 #> #> [[3]] #> [1] 17.8 16.4 17.3 15.2 10.4 #> #> [[4]] #> [1] 10.4 14.7 #> #> [[5]] #> [1] 15.5 15.2 13.3 19.2 #> #> [[6]] #> [1] 30.4 15.8 19.7 #> #> [[7]] #> [1] 15.0 21.4 #># The AccumulateCallback accumulates results from each chunk f <- function(x, pos, acc) sum(x$mpg) + acc read_csv_chunked(readr_example("mtcars.csv"), AccumulateCallback$new(f, acc = 0), chunk_size = 5)#> #> #> #> #> #> #> #> #> #> #> #> #> #>#> [1] 642.9