25356

How can I save a specified number of lines from R's history to a file?

Question:

This is a little frustrating, and I'm sure there's an easy answer.

history(max.show=N) will display N lines of history on to the terminal. savehistory(file) will save a number of lines of history to a file, depending on some environment variable. What I would like to do is

savehistory(file, max.show=N)

To do this in one line instead of having to copy or trawl through a history file for the lines I want would make things much easier.

Is there a quick function/way to save a specified number of lines to a specified file?

Answer1:

I think your best bet is to abuse the history function:

history2file <- function (fname, max.show = 25, reverse = FALSE, pattern, ...) { ## Special version of history() which dumps its result to 'fname' file1 <- tempfile("Rrawhist") savehistory(file1) rawhist <- readLines(file1) unlink(file1) if (!missing(pattern)) rawhist <- unique(grep(pattern, rawhist, value = TRUE, ...)) nlines <- length(rawhist) if (nlines) { inds <- max(1, nlines - max.show):nlines if (reverse) inds <- rev(inds) } else inds <- integer() writeLines(rawhist[inds], fname) } history2file("/tmp/bla")

I would however stimulate you to start working in script files directly, and not do stuff on the command line and then later try to piece a script together.

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