Callback classes
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.
new()
ChunkCallback$new(callback)
receive()
ChunkCallback$receive(data, index)
continue()
ChunkCallback$continue()
result()
ChunkCallback$result()
finally()
ChunkCallback$finally()
clone()
The objects of this class are cloneable with this method.
ChunkCallback$clone(deep = FALSE)
deepWhether to make a deep clone.
readr::ChunkCallback -> SideEffectChunkCallback
new()
SideEffectChunkCallback$new(callback)
receive()
SideEffectChunkCallback$receive(data, index)
continue()
SideEffectChunkCallback$continue()
clone()
The objects of this class are cloneable with this method.
SideEffectChunkCallback$clone(deep = FALSE)
deepWhether to make a deep clone.
readr::ChunkCallback -> DataFrameCallback
new()
DataFrameCallback$new(callback)
receive()
DataFrameCallback$receive(data, index)
result()
DataFrameCallback$result()
finally()
DataFrameCallback$finally()
clone()
The objects of this class are cloneable with this method.
DataFrameCallback$clone(deep = FALSE)
deepWhether to make a deep clone.
readr::ChunkCallback -> ListCallback
new()
ListCallback$new(callback)
receive()
ListCallback$receive(data, index)
result()
ListCallback$result()
finally()
ListCallback$finally()
clone()
The objects of this class are cloneable with this method.
ListCallback$clone(deep = FALSE)
deepWhether to make a deep clone.
readr::ChunkCallback -> AccumulateCallback
new()
AccumulateCallback$new(callback, acc = NULL)
receive()
AccumulateCallback$receive(data, index)
result()
AccumulateCallback$result()
clone()
The objects of this class are cloneable with this method.
AccumulateCallback$clone(deep = FALSE)
deepWhether to make a deep clone.
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)
# 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$new(f), chunk_size = 5)
# The AccumulateCallback accumulates results from each chunk
f <- function(x, pos, acc) sum(x$mpg) + acc
read_csv_chunked(readr_example("mtcars.csv"), AccumulateCallback$new(f, acc = 0), chunk_size = 5)Please choose more modern alternatives, such as Google Chrome or Mozilla Firefox.