R语言学习笔记

这里是关于一些R语言的语法备忘 Learning Website

Unit 1 Assignment and basic calculation

myapples = 3

or

myapples <- 3

+, -, *, /, ^

%% means the remainder.

Unit 2 Vectors

combine function: c()

numeric_vector = c(1,2,3) #Or c(1:3)

sum()calculates the sum of all elements of a vector. mean() calculates the average of all elements of a vector. Selection by comparison: logical comparison operator: <, >, <=, >=, ==, !=.

poker_vector[selection_vector]

Unit 3 Matrices

Useful functions: matrix(), colnames(),rownames, rbind, cbind. rowSums(), colSums(), e.g.

>matrix(1:9,byrow =TRUE, nrow = 3)
     [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6
[3,]    7    8    9

>new_hope <- c(460.998, 314.4)
>empire_strikes <- c(290.475, 247.900)
>return_jedi <- c(309.306, 165.8)
>star_wars_matrix <- matrix(c(new_hope, empire_strikes, return_jedi), nrow = 3, byrow = TRUE)
>region <- c("US", "non-US")
>titles <- c("A New Hope", "The Empire Strikes Back", "Return of the Jedi")

#Usage of colnames and rownames

>colnames(star_wars_matrix)<-region
>rownames(star_wars_matrix)<-titles

                             US non-US
A New Hope              460.998  314.4
The Empire Strikes Back 290.475  247.9
Return of the Jedi      309.306  165.8

# Usage of cbind and rbind

big_matrix <- cbind(matrix1, matrix2, vector1 ...)
big_matrix  = rbind(matrix1, ...)

注意此处与MATLAB语法的区别，在MATLAB中选取矩阵的行列用同样使用[],但是选取整列这个功能，MATLAB中使用：表示，例如school[1,:]，而在R中，不使用任何符号，例如school[1,]。

Unit 4 Factor

The term factor refers to a statistical data type used to store categorical variables. The difference between a categorical variable and a continuous variable is that a categorical variable can belong to a limited number of categories. A continuous variable, on the other hand, can correspond to an infinite number of values.

factor_speed_vector <-factor(speed_vector, ordered=TRUE, levels=c("slow","fast","insane"))

Unit 5 Data Frame

Useful fuctions show below: head(variables) shows the first observations of a data frame tail(variables) shows the last obseravations of a variables str() get a quick overview of data data.frame(vectors1, vectors2, ...) combine vectors into one data $sign: e.g. planets_df$diameter when data have names

subset(my_df, subset = some_condition), e.g. subset(planet_df, diameter<1) order()interesting function e.g.

>a = c(100,10,1000)
order(a)
[1] 2 1 3

>a[order(a),]
[1] 10 100 1000
#the comma is the solid brakets is crucial.

Unit 6 List

List can have kinds of components: vector, matrices and data frames.

My_list = list(my_vector, my_matrix, my_df)

Change the name of list

names(my_list)=c("vec", "mat", "df")

Or

my_list = list(my_vec=vec, my_matrix=mat,...)

To conveniently add elements to lists you can use the c() function, that you also used to build vectors:

ext_list <- c(my_list , my_val)

This will simply extend the original list, my_list, with the component my_val. This component gets appended to the end of the list. If you want to give the new list item a name, you just add the name as you did before:

ext_list <- c(my_list, my_name = my_val)