readr (version 2.1.2)

callback: Callback classes

Description

These classes are used to define callback behaviors.

Methods

Public methods

• ChunkCallback$new()

• ChunkCallback$receive()

• ChunkCallback$continue()

• ChunkCallback$result()

• ChunkCallback$finally()

• ChunkCallback$clone()

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Method new()

Usage

ChunkCallback$new(callback)

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Method receive()

Usage

ChunkCallback$receive(data, index)

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Method continue()

Usage

ChunkCallback$continue()

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Method result()

Usage

ChunkCallback$result()

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Method finally()

Usage

ChunkCallback$finally()

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Method clone()

The objects of this class are cloneable with this method.

Usage

ChunkCallback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Super class

readr::ChunkCallback -> SideEffectChunkCallback

Methods

Public methods

• SideEffectChunkCallback$new()

• SideEffectChunkCallback$receive()

• SideEffectChunkCallback$continue()

• SideEffectChunkCallback$clone()

Inherited methods

• readr::ChunkCallback$finally()

• readr::ChunkCallback$result()

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Method new()

Usage

SideEffectChunkCallback$new(callback)

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Method receive()

Usage

SideEffectChunkCallback$receive(data, index)

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Method continue()

Usage

SideEffectChunkCallback$continue()

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Method clone()

The objects of this class are cloneable with this method.

Usage

SideEffectChunkCallback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Super class

readr::ChunkCallback -> DataFrameCallback

Methods

Public methods

• DataFrameCallback$new()

• DataFrameCallback$receive()

• DataFrameCallback$result()

• DataFrameCallback$finally()

• DataFrameCallback$clone()

Inherited methods

• readr::ChunkCallback$continue()

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Method new()

Usage

DataFrameCallback$new(callback)

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Method receive()

Usage

DataFrameCallback$receive(data, index)

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Method result()

Usage

DataFrameCallback$result()

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Method finally()

Usage

DataFrameCallback$finally()

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Method clone()

The objects of this class are cloneable with this method.

Usage

DataFrameCallback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Super class

readr::ChunkCallback -> ListCallback

Methods

Public methods

• ListCallback$new()

• ListCallback$receive()

• ListCallback$result()

• ListCallback$finally()

• ListCallback$clone()

Inherited methods

• readr::ChunkCallback$continue()

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Method new()

Usage

ListCallback$new(callback)

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Method receive()

Usage

ListCallback$receive(data, index)

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Method result()

Usage

ListCallback$result()

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Method finally()

Usage

ListCallback$finally()

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Method clone()

The objects of this class are cloneable with this method.

Usage

ListCallback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Super class

readr::ChunkCallback -> AccumulateCallback

Methods

Public methods

• AccumulateCallback$new()

• AccumulateCallback$receive()

• AccumulateCallback$result()

• AccumulateCallback$clone()

Inherited methods

• readr::ChunkCallback$continue()

• readr::ChunkCallback$finally()

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Method new()

Usage

AccumulateCallback$new(callback, acc = NULL)

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Method receive()

Usage

AccumulateCallback$receive(data, index)

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Method result()

Usage

AccumulateCallback$result()

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Method clone()

The objects of this class are cloneable with this method.

Usage

AccumulateCallback$clone(deep = FALSE)

Arguments

deep

Whether to make a deep clone.

Details

ChunkCallback

Callback interface definition, all callback functions should inherit from this class.

SideEffectChunkCallback

Callback function that is used only for side effects, no results are returned.

DataFrameCallback

Callback function that combines each result together at the end.

AccumulateCallBack

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.

See Also

Other chunked: melt_delim_chunked(), read_delim_chunked(), read_lines_chunked()

Examples

## 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)