R语言，data

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R语言基本指令，本文主要focus在数据结构上

接上篇
本文主要是不同的数据类型以及基本的结构，主要参考的是datacamp练习

##vector

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***表示vector*** c(里面跟vector)
***name a vector***:some_vector <- c("John Doe", "poker player")
names(some_vector) <- c("Name", "Profession") 
#we will get   
    Name     Profession 
    "John Doe" "poker player" 
***比较大小***
To check if 6 is larger than 5, you type 6 > 5. This returns a logical value (TRUE or FALSE).
***选择数据***
select the first element of the vector, you type poker_vector[1].select the second element of the vector, you type poker_vector[2]
（注意顺序和python中不一样，第一个数字就type1）
***选择roulette_vector中大于0的时候***
selectionvector <- roulette_vector>0
***选择roulette_vector中大于0的时候并显示数额***
roulette_winning_days <- roulette_vector[selection_vector]

##matrix

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***form a matrix***
matrix(1:9, byrow = TRUE, nrow = 3)
box_office <- c(new_hope, empire_strikes, return_jedi) , where new_hope, empire_strikes, return_jedi are vectors
***add a name for matrix***
rownames(my_matrix) <- row_names_vector
colnames(my_matrix) <- col_names_vector
*** calculates the totals for each row of a matrix***
rowSums(my_matrix) #if sum a column, colSums()
*** add column to a matrix***
big_matrix <- cbind(matrix1, matrix2, vector1 ...)(注意顺序以及matrix的demension） #if adding a row, just use rbind
***选择数据***
my_matrix[1,2] selects the element at the first row and second column.
my_matrix[1:3,2:4] results in a matrix with the data on the rows 1, 2, 3 and columns 2, 3, 4.
my_matrix[,1] selects all elements of the first column.
my_matrix[1,] selects all elements of the first row.
***matrix运算***
2 * my_matrix multiplied every element of my_matrix by two
my_matrix1 * my_matrix2 creates a matrix where each element is the product of the corresponding elements in my_matrix1 and my_matrix2

factor

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***change the names of specific factor levels***
levels(factor_vector) <- c("name1", "name2",...)
***create an ordered factor***
you have to add two additional arguments: ordered and levels.
factor(some_vector,
       ordered = TRUE,
       levels = c("lev1", "lev2" ...))

data frames

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***insight of the data structure***
head() show the first observations of a data frame the function 
tail() prints out the last observations in your data set.
***construct a dataframe***
use data.frame()
planets_df <-data.frame(name,type,diameter,rotation,rings)
where name, type...are vectors
***select elements***
like matrix
planets_df[1:3,"type"] #look up for the first elements of column type
planets_df$diameter #select the whole diameter column
subset(planets_df, subset= diameter <1) #选择diameter<1的星球

lists

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***construct a list***
my_list <- list(comp1, comp2 ...) #comp1 comp2 are vectors
***give names to your list***
my_list <- list(name1 = your_comp1, 
                name2 = your_comp2)
or:
my_list <- list(your_comp1, your_comp2)
names(my_list) <- c("name1", "name2")
***select***
shining_list[[1]] #"grab" the first component of shining_list
shining_list[["reviews"]]
shining_list$reviews  
#The three instructions do the same
shining_list$actors[2] #choose the second element of actors