Week 1, lecture 9 notes

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+Read and Write Data - Part 2
+============================
+
+Textual Formats
+---------------
+
+* dumping and dputing are useful because the resulting textual format is editable, and in the case of corruption, potentially recoverable
+* Unlink writing out a table or CSV file, dump and dput preserve the metadata (sacrificing some readability), so that another user doesn't have to specify it all over again
+* Textual formats can work much better with version control programs like subversion and git which can only track changes meaningfully in text files
+* Textual formats can be longer-lived; if there is corruption somewhere in the file, it can be easier to fix the problem
+* Textual formats adhere to the "Unix philosophy"
+* Downside: the format is not very space efficient
+
+
+dput-ting R Objects
+-------------------
+
+Another way to pass data around is by deparsing the R object with dput and reading back using dget.
+
+	> y <- data.frame(a = 1, b = "a")
+	> dput(y)
+	structure(list(a =1,
+	               b = structure(1L, .Label = "a",
+	                             class = "factor")),
+	          .Names = c("a", "b"), row.names = c(NA, -1L),
+	          class = "data.frame")
+	> dput(y, file = "y.R")
+	> new.y <- dget("y.R")
+	> new.y
+	   a  b 
+	1  1  a
+
+
+Dumping R Objects
+-----------------
+
+Multiple objects can be deparsed using the dump function and read back in using source.
+
+	> x <- "foo"
+	> y <- data.frame(a = 1, b = "a")
+	> dump(c("x", "y"), file = "data.R")
+	> rm(x, y)
+	> source("data.R")
+	> y
+	  a  b
+	1 1  a
+	> x
+	[1] "foo"
+
+
+Interfaces to the Outside World
+-------------------------------
+
+Data are read in using connection interfaces. Connections can be made to files (most common) or to other more exotic things.
+
+* file, opens a connection to a file
+* gzfile, opens a connection to a file compressed with gzip
+* bzfile, opens a connection to a file compressed with bzip2
+* url, opens a connection to a webpage
+
+
+File Connections
+----------------
+
+	> str(file)
+	function (description = "", open = "", blocking = TRUE,
+	          encoding = getOption("encoding"))
+
+* description is the name of the file
+* open is a code indicating
+	* "r" read only
+	* "w" writing (and initializing a new file)
+	* "a" appending
+	* "rb", "wb", "ab" reading, writing, or appending in binary mode (Windows)
+
+
+Connections
+-----------
+
+In general, connections are powerful tools that let you navigate files or other external objects. In practice, we often don't need to deal with the connection interface directly.
+
+	> con <-file("foo.txt", "r")
+	> data <- read.csv(con)
+	> close(con)
+
+Is the same as:
+
+	> data <- read.csv("foo.txt")
+
+
+Reading Lines of a Text File
+----------------------------
+
+	> con <- gzfile("words.gz")
+	> x <- readLines(con, 10)
+	> x
+	[1] "1080"     "10-point" "10th"     "11-point"
+	[5] "12-point" "16-point" "18-point" "1st"
+	[9]	"2"        "20-point" ""
+
+writeLines takes a character vector and writes each element one line at a time to a text file.
+
+readLines can be useful for reading in lines of webpages.
+
+	> ## This might take time
+	> con <- url("http://www.jhsph.edu", "r")
+	> x <- readLines(con)
+	> head(x)
+	[1] "<!DOCTYPE html>"
+	[2] "<html lang=\"en\">"
+	[3] ""
+	[4] "<head>"
+	[5] "<meta charset=\"utf-8\" />"
+	[6] "<title>Johns Hopkins Bloomberg School of Public Health</title>"