callback {readr} | R Documentation |
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.
Other 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) # Print starting line of each chunk f <- function(x, pos) print(pos) read_lines_chunked(readr_example("mtcars.csv"), SideEffectChunkCallback$new(f), chunk_size = 5) # If combined results are desired you can use the DataFrameCallback # Cars with 3 gears f <- function(x, pos) subset(x, gear == 3) read_csv_chunked(readr_example("mtcars.csv"), DataFrameCallback$new(f), chunk_size = 5) # 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)