connections

R Base 3.6.2 🇮🇩 Bahasa Indonesia

Berfungsi untuk membuat, membuka dan menutup koneksi, yaitu, “file umum”, seperti file yang mungkin dikompresi, URL, pipa, dll.

Syntax

file(description = "", open = "", blocking = TRUE,
     encoding = getOption("encoding"), raw = FALSE,
     method = getOption("url.method", "default"))<p></p><p>url(description, open = "", blocking = TRUE,
    encoding = getOption("encoding"),
    method = getOption("url.method", "default"),
    headers = NULL)</p><p>gzfile(description, open = "", encoding = getOption("encoding"),
       compression = 6)</p><p>bzfile(description, open = "", encoding = getOption("encoding"),
       compression = 9)</p><p>xzfile(description, open = "", encoding = getOption("encoding"),
       compression = 6)</p><p>unz(description, filename, open = "", encoding = getOption("encoding"))</p><p>pipe(description, open = "", encoding = getOption("encoding"))</p><p>fifo(description, open = "", blocking = FALSE,
     encoding = getOption("encoding"))</p><p>socketConnection(host = "localhost", port, server = FALSE,
                 blocking = FALSE, open = "a+",
                 encoding = getOption("encoding"),
                 timeout = getOption("timeout"))</p><p>open(con, &#8230;)
# S3 method for connection
open(con, open = "r", blocking = TRUE, &#8230;)</p><p>close(con, &#8230;)
# S3 method for connection
close(con, type = "rw", &#8230;)</p><p>flush(con)</p><p>isOpen(con, rw = "")
isIncomplete(con)</p>

Arguments

Parameter	Deskripsi
`description`	character string. A description of the connection: see ‘Details’.
`open`	character string. A description of how to open the connection (if it should be opened initially). See section ‘Modes’ for possible values.
`blocking`	logical. See the ‘Blocking’ section.
`encoding`	The name of the encoding to be assumed. See the ‘Encoding’ section.
`raw`	logical. If true, a ‘raw’ interface is used which will be more suitable for arguments which are not regular files, e.g.character devices. This suppresses the check for a compressed file when opening for text-mode reading, and asserts that the ‘file’ may not be seekable.
`method`	character string, partially matched to c("default", "internal", "wininet", "libcurl"): see ‘Details’.
`headers`	named character vector of HTTP headers to use in HTTP requests. It is ignored for non-HTTP URLs. The User-Agent header, coming from the HTTPUserAgent option (see options) is used as the first header, automatically.
`compression`	integer in 0--9. The amount of compression to be applied when writing, from none to maximal available. For xzfile can also be negative: see the ‘Compression’ section.
`timeout`	numeric: the timeout (in seconds) to be used for this connection. Beware that some OSes may treat very large values as zero: however the POSIX standard requires values up to 31 days to be supported.
`filename`	a filename within a zip file.
`host`	character string. Host name for the port.
`port`	integer. The TCP port number.
`server`	logical. Should the socket be a client or a server?
`con`	a connection.
`type`	character string. Currently ignored.
`rw`	character string. Empty or "read" or "write", partial matches allowed.
`…`	arguments passed to or from other methods.

Return Value

file, pipe, fifo, url, gzfile, bzfile, xzfile, unz dan socketConnection mengembalikan objek koneksi yang mewarisi dari kelas "koneksi" dan memiliki kelas pertama yang lebih spesifik. buka dan siram kembalikan NULL, tanpa terlihat. close mengembalikan status NULL atau integer, tanpa terlihat. Statusnya adalah dari saat koneksi terakhir kali ditutup dan hanya tersedia untuk beberapa jenis koneksi (misalnya pipa, file, dan fifos): biasanya nilai nol menunjukkan keberhasilan. Nilai negatif akan menghasilkan peringatan; jika menulis

Details

Sembilan fungsi pertama membuat koneksi. Secara default, koneksi tidak dibuka (kecuali untuk socketConnection), tetapi dapat dibuka dengan menyetel nilai argumen terbuka yang tidak kosong. Untuk file, deskripsinya adalah jalur ke file yang akan dibuka atau URL lengkap (jika sama dengan url pemanggil), atau "" (default) atau "papan klip" (lihat bagian 'Papan Klip'). Gunakan "stdin" untuk merujuk pada 'input standar' tingkat C dari proses (yang tidak perlu dihubungkan ke apa pun di konsol atau versi R yang tertanam, dan tidak ada di RGui di Windows). Lihat juga stdin() untuk konsep stdin level R yang sedikit berbeda. Lihat nullfile() untuk cara platform-independen untuk mendapatkan nama file perangkat null. Untuk url deskripsinya adalah URL lengkap termasuk skemanya (seperti http://, https://, ftp:// atau file://)

Contoh

Example

# NOT RUN {
zzfil <- tempfile(fileext=".data")
zz <- file(zzfil, "w")  # open an output file connection
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = zz, sep = "\n")
cat("One more line\n", file = zz)
close(zz)
readLines(zzfil)
unlink(zzfil)

zzfil <- tempfile(fileext=".gz")
zz <- gzfile(zzfil, "w")  # compressed file
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = zz, sep = "\n")
close(zz)
readLines(zz <- gzfile(zzfil))
close(zz)
unlink(zzfil)
zz # an invalid connection

zzfil <- tempfile(fileext=".bz2")
zz <- bzfile(zzfil, "w")  # bzip2-ed file
cat("TITLE extra line", "2 3 5 7", "", "11 13 17", file = zz, sep = "\n")
close(zz)
zz # print() method: invalid connection
print(readLines(zz <- bzfile(zzfil)))
close(zz)
unlink(zzfil)

## An example of a file open for reading and writing
Tpath <- tempfile("test")
Tfile <- file(Tpath, "w+")
c(isOpen(Tfile, "r"), isOpen(Tfile, "w")) # both TRUE
cat("abc\ndef\n", file = Tfile)
readLines(Tfile)
seek(Tfile, 0, rw = "r") # reset to beginning
readLines(Tfile)
cat("ghi\n", file = Tfile)
readLines(Tfile)
Tfile # -> print() :  "valid" connection
close(Tfile)
Tfile # -> print() :  "invalid" connection
unlink(Tpath)

## We can do the same thing with an anonymous file.
Tfile <- file()
cat("abc\ndef\n", file = Tfile)
readLines(Tfile)
close(Tfile)

# }
# NOT RUN {
## fifo example -- may hang even with OS support for fifos
if(capabilities("fifo")) {
  zzfil <- tempfile(fileext="-fifo")
  zz <- fifo(zzfil, "w+")
  writeLines("abc", zz)
  print(readLines(zz))
  close(zz)
  unlink(zzfil)
}
# }
# NOT RUN {
## Unix examples of use of pipes

# read listing of current directory
readLines(pipe("ls -1"))

# remove trailing commas.  Suppose
oldwd <- setwd(tempdir())
writeLines(c("450, 390, 467, 654,  30, 542, 334, 432, 421,",
"357, 497, 493, 550, 549, 467, 575, 578, 342,",
"446, 547, 534, 495, 979, 479"), "data2_")
% cat data2_
450, 390, 467, 654,  30, 542, 334, 432, 421,
357, 497, 493, 550, 549, 467, 575, 578, 342,
446, 547, 534, 495, 979, 479
# Then read this by
scan(pipe("sed -e s/,$// data2_"), sep = ",")
unlink("data2_"); setwd(oldwd)

# convert decimal point to comma in output: see also write.table
# both R strings and (probably) the shell need \ doubled
zzfil <- tempfile("outfile")
zz <- pipe(paste("sed s/\\\\./,/ >", zzfil), "w")
cat(format(round(stats::rnorm(48), 4)), fill = 70, file = zz)
close(zz)
file.show(zzfil, delete.file = TRUE)
# }
# NOT RUN {
## example for a machine running a finger daemon

con <- socketConnection(port = 79, blocking = TRUE)
writeLines(paste0(system("whoami", intern = TRUE), "\r"), con)
gsub(" *$", "", readLines(con))
close(con)
# }
# NOT RUN {
# }
# NOT RUN {
## Two R processes communicating via non-blocking sockets
# R process 1
con1 <- socketConnection(port = 6011, server = TRUE)
writeLines(LETTERS, con1)
close(con1)

# R process 2
con2 <- socketConnection(Sys.info()["nodename"], port = 6011)
# as non-blocking, may need to loop for input
readLines(con2)
while(isIncomplete(con2)) {
   Sys.sleep(1)
   z <- readLines(con2)
   if(length(z)) print(z)
}
close(con2)

## examples of use of encodings
# write a file in UTF-8
cat(x, file = (con <- file("foo", "w", encoding = "UTF-8"))); close(con)
# read a 'Windows Unicode' file
A <- read.table(con <- file("students", encoding = "UCS-2LE")); close(con)
# }