『Data Science』R语言学习笔记，基础语法

Multiple objects can be deparsed using the dump function and read back in using source.

> x <- "foo"                          ## create the first data object
> y <- data.frame(a = 1,b = "a")     ## create the second data object
> dump(c("x","y"),file = "data.R")  ## store the both data object in to a file called 'data.R'
> rm(x,y)                            ## remove the both data object from RAM
> source("data.R")                    ## import the dumped file 'data.R'
> y                                   ## print the data object 'y' from 'data.R'
  a b
1 1 a
> x                                   ## print the data object 'x' from 'data.R'
[1] "foo"

Connections: 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.

> con <- file('db.txt','r')
> readLines(con)

Subsetting

• [always returns an object of the same class as the original; can be used to select more than one element (there is one exception)
• [[is used to extract elements of a list or a data frame; it can only be used to extract a single element and the class of the returned object will not necessarily be a list or data frame.
• $ is used to extract elements of a list or data frame by name; semantics are similar to hat of [[.

Basic

> x <- c("a","c","d","e")
> x[1]
[1] "a"
> x[2]
[1] "b"
> x[1:3]
[1] "a" "b" "c"
> x[x > "a"]
[1] "b" "c" "d" "e"
> u  <- x>"a"
> u
[1] FALSE  TRUE  TRUE  TRUE  TRUE
> x[u]
[1] "b" "c" "d" "e"

Lists

> x <- list(foo = 1:4,bar = 0.6)

> x[1]
$foo
[1] 1 2 3 4
> x[[1]]
[1] 1 2 3 4
> x[[2]]
[1] 0.6

> x$bar
[1] 0.6
> x$foo
[1] 1 2 3 4

> x[["bar"]]
[1] 0.6
> x["bar"]
$bar
[1] 0.6

> x <- list(foo = 1:4,bar = 0.6,baz = "hello")

> x[c(1,3)]
$foo
[1] 1 2 3 4
$baz
[1] "hello"

> name <- "foo"
> x[[name]]
[1] 1 2 3 4
> x$name          ## `name` is a variable,not a `level`,so does not has x$name in the list `x`.
NULL
> x$foo
[1] 1 2 3 4

Matrices

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