windows - Reading the last n lines from a huge text file -


i've tried 

file_in <- file("myfile.log","r") x <- readlines(file_in, n=-100)

but i'm still waiting...

any appreciated

i'd use scan this, in case know how many lines log has :

scan("foo.txt",sep="\n",what="char(0)",skip=100)

if have no clue how many need skip, have no choice move towards either

  • reading in , taking last n lines (in case that's feasible),
  • using scan("foo.txt",sep="\n",what=list(null)) figure out how many records there are, or
  • using algorithm go through file, keeping last n lines every time

the last option :

readlastlines <- function(x,n,...){       con <- file(x)   open(con)   out <- scan(con,n,what="char(0)",sep="\n",quiet=true,...)    while(true){     tmp <- scan(con,1,what="char(0)",sep="\n",quiet=true)     if(length(tmp)==0) {close(con) ; break }     out <- c(out[-1],tmp)   }   out }

allowing :

readlastlines("foo.txt",100)

or

readlastlines("foo.txt",100,skip=1e+7)

in case know have more 10 million lines. can save on reading time when start having extremely big logs.

edit : in fact, i'd not use r this, given size of file. on unix, can use tail command. there windows version well, somewhere in toolkit. didn't try out yet though.


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