http://cran.rstudio.com 下载并安装 R 编程语言。
http://www.rstudio.com 下载并安装 RStudio。
create the vector 'udacious':
udacious <- c("Chris Saden", "Lauren Castellano",
"Sarah Spikes","Dean Eckles",
"Andy Brown", "Moira Burke",
"Kunal Chawla")
udacious
numbers <- c(1:10)
numbers
numbers <- c(numbers, 11:20) #add values to a vector
numbers
mystery is a vector that contains the number of characters for each of the names in udacious.
mystery = nchar(udacious)
mystery
Here we get a logical (or boolean) vector that tells us which locations or indices in the vector contain a name that has exactly 11 characters.
mystery == 11
udacious[mystery == 11]
data(mtcars) #load the mtcars data,
names(mtcars) #返回列名
?mtcars #the details and documentation will appear in the 'Help' tab.
mtcars # the entire data frame printed out.
str(mtcars) #gives us the structure of the data frame
#'data.frame': (行数) obs. of (列数)variables:
#lists the variable names, #
#the type of each variable and some values for each variable.
dim(mtcars) #返回行数和列数
row.names(mtcars) #the current row names in the data frame.
row.names(mtcars) <- c(1:32) #change the row names of the cars to numbers.
data(mtcars) #reload the data set
head(mtcars, 10) #print out the first ten rows.
head(mtcars) #The head() function prints out the first six rows
#of a data frame by default.
tail(mtcars, 3) #print out the last three rows.
mtcars$mpg #access an individual column from the data
#frame （仅包含这一列的所有值）
mean(mtcars$mpg) #get the average mpg for all the cars.
平均值示例
x <- c(0:10, 50)
x
xm <-mean(x)
xm #output:[1] 8.75
c(xm, mean(x, trim = 0.10)) #output:[1] 8.75 5.50
trim表示截尾平均数，0~0.5之间的数值，如：0.10表示丢弃最大10%和最小的10%的数据后，再计算算术平均数。默认为0.
