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use writeLines for fread(text=.) #4805

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May 11, 2021
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use writeLines for fread(text=.) #4805

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2 changes: 1 addition & 1 deletion R/fread.R
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Original file line number Diff line number Diff line change
Expand Up @@ -35,7 +35,7 @@ yaml=FALSE, autostart=NA, tmpdir=tempdir(), tz="")
if (!is.character(text)) stop("'text=' is type ", typeof(text), " but must be character.")
if (!length(text)) return(data.table())
if (length(text) > 1L) {
cat(text, file=(tmpFile<-tempfile(tmpdir=tmpdir)), sep="\n") # avoid paste0() which could create a new very long single string in R's memory
writeLines(text, tmpFile<-tempfile(tmpdir=tmpdir)) # avoid paste0() which could create a new very long single string in R's memory
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We could also use useBytes=TRUE here to facilitate writing UTF-8 strings on Windows:

https://stackoverflow.com/q/10675360/3576984

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@mrdwab mrdwab Jan 6, 2021 •
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@MichaelChirico This isn't something I've tested, but maybe fwrite(as.data.table(text), tmpFile<-tempfile(tmpdir = tmpdir), col.names = FALSE) is also worth exploring. I'm basing this assumption on the speed that I observed here.

Or maybe list(text) instead of as.data.table(text) since fwrite should work with that too..?

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In general I think it may warrant some benchmarking. Actually I have run into an issue recently where cat() is very slow for long input. In my case I was cat-ing a whole file by character (e.g. cat(strsplit(readChar(f, file.size(f)), NULL)[[1]], sep = '', file = f) is quite slow)

file = tmpFile
on.exit(unlink(tmpFile), add=TRUE)
} else {
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