R shortcuts

Question 1

cmd + shft + c

Answer 1

To comment multiple code in R studio

Question 2

u can use both for assigment?

Answer 2

equality and < sign

Question 3

?funcname does what?

Answer 3

open windows with what the function does

Question 4

ls() list what?

Answer 4

list of all of the objects

Question 5

rm() ? What differ list and remove functions?

Answer 5

remove object that we dont want e.g rm(x,y)

Question 6

how to remove all objects at once?

Answer 6

rm(list=ls())

Question 7

?matrix ?

Answer 7

The help file reveals that the matrix() function takes a number of inputs, but for now we focus on the first three: the data (the entries in the matrix), the number of rows, and the number of columns. First, we create a simple matrix

x=matrix(data=c(1,2,3,4), nrow=2, ncol=2)

Note that we could just as well omit typing data=, nrow=, and ncol= in the matrix() command above: that is, we could just type
> x=matrix(c(1,2,3,4) ,2,2)

Question 8

by default matrix create by colum, how to create it by rows?

Answer 8

R creates matrices by successively filling in columns. Alternatively, the byrow=TRUE option can be used to populate the matrix in order of the rows.
> matrix(c(1,2,3,4),2,2,byrow=TRUE)

Question 9

sqrt(x)

Answer 9

calculate squaroot of X

Question 10

rnorm()

Answer 10

generates a vector of random normal variables, with first argument n the sample size. Each time we call this function, we will get a different answer.

By default, rnorm() creates standard normal random variables with a mean of 0 and a standard deviation of 1. However, the mean and standard devi- ation can be altered using the mean and sd arguments, as illustrated above

x=rnorm(50)
y=x+rnorm(50,mean=50,sd=.1)

Question 11

how to use set.seed() to create same random result ?

Answer 11

Sometimes we want our code to reproduce the exact same set of random numbers; we can use the set.seed() function to do this. The set.seed() function takes an (arbitrary) integer argument.

Question 12

Plot

Answer 12

plot() function is the primary way to plot data in R

passing in the argument xlab will result in a label on the x-axis.

> plot(x,y)
plot(x,y,xlab=”this is the x-axis”,ylab=”this is the y-axis”,
main=”Plot of X vs Y”)

Question 13

dev.off() it does what?

Answer 13

dev.off() indicates to R that we are done creating the plot.

Question 14

seq(a,b)

Answer 14

creates sequence of numbers

seq(0,1,length=10) makes a sequence of 10 numbers that are equally spaced between 0 and 1

Question 15

indexing A[2,3]

Answer 15

The first number after the open-bracket symbol [ always refers to the row, and the second number always refers to the column.

A[c(1,3),c(2,4)]
A[1:3,2:4]
A [1:2 ,]
A [ ,1:2]

The last two examples include either no index for the columns or no index for the rows. These indicate that R should include all columns or all rows, respectively. R treats a single row or column of a matrix as a vector

Question 16

A[-c(1,3),] What does this means ?

Answer 16

The use of a negative sign - in the index tells R to keep all rows or columns except those indicated in the index.

Question 17

dim (A)?

Answer 17

The dim() function outputs the number of rows followed by the number of columns of a given matrix.

Question 18

read.table() ?

Answer 18

primary way to import data

Question 19

write.table() ?

Answer 19

We can use the function write.table() to export data.

Question 20

What is data frame?

Answer 20

R store objects in a form called Data Frame

Question 21

persp() can be use to create three dimentional plot

Answer 21

persp() can be used to produce a three-dimensional

plot.

Question 22

Option + ‘-‘?

Answer 22

shorcut for input operator in r

Question 23

read.csv()

Answer 23

easiest way to load data in R

Question 24

hearder = T in read.csv why ?

Answer 24

Using the option header=T (or header=TRUE) in the read.table() function tells R that the first line of the file contains the variable names,

Question 25

na.strings in read.csv why ?

Answer 25

na.strings tells R that any time it sees a particular character or set of characters (such as a question mark), it should be treated as a missing element of the data matrix

Question 26

e na.omit(

Auto=na.omit(Auto)

Answer 26

There are various ways to deal with the missing data. In this case, only five of the rows contain missing observations, and so we choose to use the na.omit() function to simply remove these rows.

Question 27

names() function what it is used?

Answer 27

use to print names of the variable names

Question 28

Why variables use $? and what is diff $ and attach()

Answer 28

To refer to a variable, we must type the data set and the variable name joined with a $ symbol

Alternatively, we can use the attach() function in order to tell R to make the variables in this data frame available by name

> plot(Auto$cylinders , Auto$mpg )
attach(Auto)
plot(cylinders , mpg

Question 29

how to convert quantitative variavle to qualitative variables?

Answer 29

The as.factor() function converts quantitative variables into qualitative variables.

cylinders=as.factor(cylinders)

The cylinders variable is stored as a numeric vector, so R has treated it as quantitative. However, since there are only a small number of possible values for cylinders, one may prefer to treat it as a qualitative variable

Question 30

hist()

Answer 30

can be use to create histogram

e.g his(mpeg , )

Question 31

pairs()

Answer 31

creates scatter plot matrix

Question 32

summary() function ?

Answer 32

The summary() function produces a numerical summary of each variable in a particular data set. we can also produce summary of a single variable

Question 33

exiting R how ?

Answer 33

type q()

Question 34

savehistory()

Answer 34

Before exiting R, we may want to save a record of all of the commands that we typed in the most recent session; this can be accomplished using the savehistory() function

Question 35

loadhistory()

Answer 35

Next time we enter R, we can load that history using the loadhistory() function.