Data frame
What's a data frame?
A data frame has the variables of a data set as columns and the observations as rows.
data frame matrix
mtcars
head(mtcars)
tail(mtcars)
str(mtcars) structure of your data set
Creating a data frame
# Definition of vectors
name <- c("Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune") type <- c("Terrestrial planet", "Terrestrial planet", "Terrestrial planet",
"Terrestrial planet", "Gas giant", "Gas giant", "Gas giant", "Gas giant") diameter <- c(0.382, 0.949, 1, 0.532, 11.209, 9.449, 4.007, 3.883)
rotation <- c(58.64, -243.02, 1, 1.03, 0.41, 0.43, -0.72, 0.67) rings <- c(FALSE, FALSE, FALSE, FALSE, TRUE, TRUE, TRUE, TRUE)
# Create a data frame from the vectors
planets_df <- data.frame( name, type, diameter, rotation, rings) planets_df
str(planets_df)
Selection of data frame elements
# Print out diameter of Mercury (row 1, column 3)
planets_df[1,3]
planets_df[4, ]
planets_df[6:8, "diameter"]
planets_df[ , "type"]
[row, column]
Selection of data frame elements
# Print out diameter of Mercury (row 1, column 3)
planets_df[1,3]
planets_df[4, ]
planets_df[6:8, "diameter"]
planets_df[ , "type"]
planets_df$type
[row, column]
條件篩選
subset(planets_df, subset = diameter < 2) subset(planets_df, subset = rings )
subset(planets_df, subset = name ) 只能是 logical 型態
Sorting
a <- c(100, 10, 1000)
order(a)
a[order(a)]
Sorting data frame
positions <- order(planets_df$diameter)
◦ 根據 diameter 排序
planets_df[positions, ]
Summary
Vectors (one dimensional array): can hold numeric, character or logical va lues. The elements in a vector all have the same data type.
Matrices (two dimensional array): can hold numeric, character or logical v alues. The elements in a matrix all have the same data type.
Data frames (two-dimensional objects): can hold numeric, character or lo gical values. Within a column all elements have the same data type, but di fferent columns can be of different data type.
List
list()
# Vector with numerics from 1 up to 10 my_vector <- 1:10
# Matrix with numerics from 1 up to 9 my_matrix <- matrix(1:9, ncol = 3)
# First 10 elements of the built-in data frame mtcars my_df <- mtcars[1:10,]
# Construct list with these different elements:
my_list <- list(my_vector, my_matrix, my_df) my_list
list() 加上別名
# Vector with numerics from 1 up to 10 my_vector <- 1:10
# Matrix with numerics from 1 up to 9 my_matrix <- matrix(1:9, ncol = 3)
# First 10 elements of the built-in data frame mtcars my_df <- mtcars[1:10,]
# Adapt list() call to give the components names
my_list <- list(vec = my_vector, mat = my_matrix, df = my_df) my_list
用別名取出元素
my_vector <- 1:10
my_matrix <- matrix(1:9, ncol = 3) my_df <- mtcars[1:10,]
my_list <- list(vec = my_vector, mat = my_matrix, df = my_df)
my_list["mat"]
my_list[["mat"]]
my_list$mat
Add value(s) to the list
my_vector <- 1:10
my_matrix <- matrix(1:9, ncol = 3) my_df <- mtcars[1:10,]
my_list <- list(vec = my_vector, mat = my_matrix, df = my_df)
my_list <- c(my_list, year = 1980, month = 11) my_list
