Reads the specified file block by block and feeds each block to the specified function.
process_blocks(x, fun, ...)# S4 method for laf
process_blocks(
x,
fun,
columns = 1:ncol(x),
nrows = 5000,
allow_interupt = FALSE,
progress = FALSE,
...
)
an object the supports the process_blocks method, such as an
laf object.
a function to apply to each block (see details).
additional parameters are passed on to fun.
an integer vector with the columns that should be read in.
the (maximum) number of rows to read in one block
when TRUE the function fun is expected to
return a list. The second element is the result of the function. The first
element should be a logical value indication whether process_blocks
should continue (FALSE) or stop (TRUE). When interrupted the function is
not called a last time with an empty data.frame to finalize the
result.
show a progress bar. Note that this triggers a calculation
of the number of lines in the file which for CSV files can take some time.
When numeric code is used as the style of the progress bar (see
txtProgressBar).
The function should accept as the first argument the next block of data. When
the end of the file is reached this is an empty (zero row) data.frame.
As the second argument the function should accept the output of the previous
call to the function. The first time the function is called the second
argument has the value NULL.