Study of R

5 minute read

I think this notes may help me to get better understanding of R.

help

You can type these codes to help you to understand the function which R is provided

# get the help of function
help(functionName)
# get the args of one function
args(functionName)
# get example of one function
example(functionName)

# Or you can use opeaator '?' which is same as help
?functionname

Or perhaps you don’t know the exactly name of function, you can use these:

help.search(partOfFunctionName)
# Or
??partOfFunctionName

If you want some details, or your computer dosen’t have the document of R. you can type this code:

RSiteSearch(functionName)

R

In fact, some constant values or functions you can type the name at will:

pi
[1] 3.141593
sqrt(2)
[1] 1.414214

When you enter expressions like that, R evaluates the expression and then implicitly calls the print function By the way, you can also write down the code print() to print the value of variable.

Vector

In your task, maybe you will find your sometime, data has miss one or two value, you can use NA to replace it. if you do this. be sure to use na.rm=TRUE For example, When you use the function to calculate the average

x <- c(0,1,1,2,3,NA)
mean(x, na.rm=TRUE)

Sequence

To create the simple sequence n, n+1, n+2, …, m. You can use two different way to initialize a sequence:

use operator : with two numbers. the first one means the begin of the sequence, the last one means the end of this sequence.
or you can type all this function name seq to build a sequence. using from as the begin, and to as the end of the sequence.

The sequence default the step is 1, if you want to change special step, use by to change it.

1:5
# [1] 1 2 3 4 5
seq(from=1, to=5, by=2)
# [1] 1 3 5

In some time you don’t know the exactly the step which you need. you can use length.out = #step# #step# you can replace it as the count Which you want get in Vector or Sequence. The R will calculate the step.

seq(from=0, to=20, length.out=5)
# [1] 0 5 10 15 20

If you want to create repeated sequence, you must use req to initialize

rep(1, times=5)
# [1] 1 1 1 1 1

Compare

The R can compare between numbers, squence or vector. even number and squence. In that case the only number will compare the value from vector, one by one. and the operator is same as C. using the <, >, >=, <=, ==, !=. for example:

x <- c(3,4,4)
v <- 2
x == v
# [1] FALSE FALSE FALSE

Get the value

The way to get value from Vector or Squence is same as C.

x <- seq(from=1, to=5)
x[1]
# [1] 1

Selecting Vector Elements

It’s same as python.

fib <- c(0,1,1,2,3,5,8,13,21,34)
fib[c(1,2,4,8)]
# [1] 0 1 2 13

Be care How to deal with [-1] R is different from Python. Cheak the different:

fib[1:3]
# [1] 0 1 1
fib[-(1:3)] 
# [1] 2 3 5 8 13 21 34

In python -index, means that is a value, which The penultimate index of Vector or Sequence. But In R, -index, means the index in Vector or Sequence will be ignored.

Operator

<-

assign a value to name syntax:

# These are same
name <- value
value -> name

And <- means the local variable, when you want to use the global variable, you should use <<-

c

Use the c() to initialize a vector. You can not use C.

c(1,1,2,3,5,8,13,21)
# [1] 1 1 2 3 5 8 13 21
v1 <- c(1,2,3)
v3 <- c("A","B","C")
c(v1,v3)
# [1] "1" "2" "3" "A" "B" "C"

Be Care

when you give different type in one vector, R will change some types, to make all the types are same. for example is case below, the vector has two different types, numeric, character. Before creating the vector, thereby(从而) making the data elements compatible(兼容).

mode(3.1415)
# [1] "numeric"
mode("foo")
# [1] "character"
c(3.1415, "foo")
# [1] "3.1415" "foo"
mode(c(3.1415, "foo"))
# "character"

function

cat

Use this funcation to combine multiple items into one string. Be noticed that the cat put one space between each items. for example:

cat("The zero occurs at", 2*pi, "radians.", "\n")
# The zero occurs at 6.283185 radians.

You must provide a newline character (\n) to terminate the line.
A serious limitation is that it cannot print compound(夝坈) data structures such as matrices and lists.

ls()

The function displays the name of object in workspace. or you can yuo ls.str() to show more details.

# if you workspace is empty
ls()
# character(0)
x <- 3
ls()
# [1] "x"
# use ls.str() to get more details
ls.str()
# x :  num 3

AddSomeThing

The variables which begins with a dot(.) name are considered hidden and are not and are not normally of interest to users

.x <-10
ls()
# character(0)

but you can use ls(all.name=TRUE) to show all variables include the hiddened one. R is Case sensitive

rm()

Remove the variables. for example

x <- 10
rm(x)
ls()
# character(0)

if you want to remove all variables, use rm(list=ls())

Never put rm(list=ls()) into code you share with others, such as a library function or sample code sent to a mailing list. Deleting all the variables in someone else’s workspace is worse than rude and will make you extremely unpopular.

mode()

To cheak the type of variables.

mode(3.14)
# [1] "numeric"

Vector Math Function

mean (average value)
median
standard deviation
variance (方差)
correlation (相关系数)
covariance (坝方差) use these function below: • mean(x) • median(x) • sd(x) • var(x) • cor(x, y) • cov(x, y)

names()

Give the squence or vector every column a name. if you do not give enough names, R will give that column named <NA> Then you can just use name to get the value.

v <- c("123", "123", "123")
names(v)<-c("test1")
v
# test1  <NA>  <NA> 
# "123" "123" "123" 

v["test1"]
# test1 
# "123" 

Packages

You can use Packages to help you finish a lot of things more easily.

# This funcation will show all the function support in the libray
libray()
# Or you can use the code below
install.packages()[,c("Package", "Version")]

Share on

Twitter Facebook LinkedIn

Your Name