How to get commands history as a character vector instead of displaying them?

Hi Everyone,

I want to get the commands history as a character vector instead of
just displaying them, but the function history() just returns NULL. I
checked the source code of 'history' and could not find a solution.
Anybody has an idea? Thanks!
  

P. S. My original problem is, when a user opens a graphics device like
png() or pdf(), I want to know the file name used by this device. I
thought history() would help, but it could not.

  

sessionInfo()
    

R version 2.8.1 (2008-12-22)
i386-pc-mingw32

locale:
LC_COLLATE=Chinese_People's Republic of
China.936;LC_CTYPE=Chinese_People's Republic of
China.936;LC_MONETARY=Chinese_People's Republic of
China.936;LC_NUMERIC=C;LC_TIME=Chinese_People's Republic of China.936

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

Regards,
Yihui
--
Yihui Xie <xieyihui at gmail.com>
Phone: +86-(0)10-82509086 Fax: +86-(0)10-82509086
Mobile: +86-15810805877
Homepage: http://www.yihui.name
School of Statistics, Room 1037, Mingde Main Building,
Renmin University of China, Beijing, 100872, China

Hi Everyone,

I want to get the commands history as a character vector instead of
just displaying them, but the function history() just returns NULL. I
checked the source code of 'history' and could not find a solution.
Anybody has an idea? Thanks!

P. S. My original problem is, when a user opens a graphics device like
png() or pdf(), I want to know the file name used by this device. I
thought history() would help, but it could not.

sessionInfo()

R version 2.8.1 (2008-12-22)
i386-pc-mingw32

locale:
LC_COLLATE=Chinese_People's Republic of
China.936;LC_CTYPE=Chinese_People's Republic of
China.936;LC_MONETARY=Chinese_People's Republic of
China.936;LC_NUMERIC=C;LC_TIME=Chinese_People's Republic of China.936

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

Regards,
Yihui
--
Yihui Xie <xieyihui at gmail.com>
Phone: +86-(0)10-82509086 Fax: +86-(0)10-82509086
Mobile: +86-15810805877
Homepage: http://www.yihui.name
School of Statistics, Room 1037, Mingde Main Building,
Renmin University of China, Beijing, 100872, China

Yihui Xie wrote:

Hi Everyone,

I want to get the commands history as a character vector instead of
just displaying them, but the function history() just returns NULL. I
checked the source code of 'history' and could not find a solution.
Anybody has an idea? Thanks!
  

history eventually calls file.show, which will use the pager option to
determine how to show the file, so you can do something like that:

history <- function( ... ){
old.op <- options( pager = function( files, header, title, delete.file
) readLines( files ) ); on.exit( options( old.op ) )
utils::history(...)
}
history( pattern = "png" )

Romain Francois wrote:

Yihui Xie wrote:

Hi Everyone,

I want to get the commands history as a character vector instead of
just displaying them, but the function history() just returns NULL. I
checked the source code of 'history' and could not find a solution.
Anybody has an idea? Thanks!

history eventually calls file.show, which will use the pager option to
determine how to show the file, so you can do something like that:

history <- function( ... ){
old.op <- options( pager = function( files, header, title, delete.file
) readLines( files ) ); on.exit( options( old.op ) )
utils::history(...)
}
history( pattern = "png" )

i think the following is an acceptable alternative:

? ?history = function() {
? ? ? file = tempfile()
? ? ? on.exit(unlink(file))
? ? ? savehistory(file)
? ? ? readLines(file) }

the output is *lines* of text, but if you need whole executable
expressions, you can parse the output:

? ?1 + 1
? ?ph = parse(text=history())
? ?as.list(ph)
? ?ph[length(ph)-1]
? ?# expression(1 + 1)
? ?eval(ph[length(ph)-1])
? ?# [1] 2


vQ