name <- c("A","B","C","D","E","F","G","H","I","J")
age <- c(22,43,12,17,29,5,51,56,9,44)
sex <- c("M","F","M","M","M","F","F","M","F","F")

undertaker <- data.frame(name,age,sex,stringsAsFactors=FALSE)
undertaker

str(undertaker)# view the properties

#data frame name $ variable name

undertaker$name <- as.character(undertaker$name)
undertaker$sex <- as.character(undertaker$sex)

rock <- undertaker

rock[1]# only the number refers to column index

# right hand side of the comma is for columns
# left hand side of the comma is for rows

rock[,c(1,3)]## you can specify the columns by index
rock[,c("name","age")]## you can specify the columns by name

rock[1:5,c(1,3)]## you can specify the rows by index

rock[c(1:5),]## you can specify the rows by index

head(rock)# top 6 rows with all columns
head(rock,7)# top 2 rows with all columns

tail(rock,2)# bottom 2 rows


attach(rock)
rock[age > 20,]# greater than
rock[age >= 22,]# greater than equals to
rock[age <= 22,]# less than equals to

rock[name == "A",c("age","name")]# equals to

rock[name == "A",c("age","name")]# equals to

rock[name != "D",]# not equals to

rock[sex == "F" & age < 50,]# and condition

rock[sex == "F" | name == "A",]# or condition


## shortcut of using or function
rock[rock$name == "A" | rock$name == "B",]


rock[rock$name %in% c("A","B"),]