Input/output

1. Input
   • Read a table from a file
   • Download a file from the Internet
   • Read lines from a web page
2. Output

Input

Read a table from a file

Read a tab-separated file. Always provide stringAsFactors, row.names and header.

read.table("file.dat", header = TRUE, row.names = NULL, stringsAsFactors = FALSE)

Download a file from the Internet

The download.file() function can be used to dowload a file from the Internet. A particular attention should be taken if the protocol is secured (https). Then other methods than the default should be used (wget or curl) or the user will get a “unsupported url scheme” error.

download.file("https://www.data.gouv.fr/var/download/6c0c22473a289c426bca9aecb9b6e21c.zip", 
    destfile = "~/produitsBiocides2011.csv", method = "wget")

Read lines from a web page

In order to read a web page directly, one should first open a connexion to the web page giving a URL. Then this connexion is used to read a given number of lines. n=-1L is the default value and means that everything will be read, but one can also provide a specific number of lines.)

url <- url("http://www.google.com/")
googleMainPage <- readLines(url, n = -1)

## Warning: ligne finale incomplète trouvée dans 'http://www.google.com/'

length(googleMainPage)

## [1] 17

close(con = url)

Output

Write a table

With the write.table() function. By default it uses tabulation as separator. Row names are also saved. Consequently, the first line has one element less than following lines.

dframe <- data.frame(a = c(1, 5, 3), b = c("blue", "red", "green"))
write.table(dframe, "dataframe.txt", append = FALSE, sep = "\t", row.names = FALSE, 
    quote = FALSE, col.names = FALSE)

This work by Celine Hernandez is licensed under a Creative Commons Attribution-ShareAlike 3.0 Unported License.