问题
I'm using readr::read_lines_chunked
in the following way:
if(!require(readr)) install.packages("readr", repos = "http://cran.us.r-project.org")
mytb <- NULL
read_lines_chunked(file="/tmp/huge.xml", chunk_size=10, callback = function(xml, pos) {
// extract values from xml into tmp
if (is.null(mytb)) {
users <- as_tibble(tmp)
} else {
users <- bind_rows(users, as_tibble(tmp))
}
})
but this doesn't work as mytb
always ends up being null
... how do you accumulate the results into a tibble?
回答1:
I found the solution. This package has a group of callback handlers that wrap the custom handler. So this is how it works:
mytb <- read_lines_chunked(file="/tmp/huge.xml", chunk_size=10, callback = DataFrameCallback$new(function(xml, pos) {
// extract values from xml into tmp
as_tibble(tmp)
}))
Note the DataFrameCallback$new(...)
decorator and returning the tibble I want to stitch together as rbind
.
来源:https://stackoverflow.com/questions/59314478/how-to-accumulate-the-results-of-readrread-lines-chunked