0202dataframe.R

#將向量資料組合為data frame(數據框)
#建立向量
id <- c("001", "002", "003", "004", "005")
name <- c("superman", "batman", "spiderman", "wolverine", "wonderwoman")
height <- c(190, 188, 178, 150, 183)
weight <- c(102, 95, 76, 88, 59)
gender <- c("Male", "Male", "Male", "Male", "Female")
id

## [1] "001" "002" "003" "004" "005"

height

## [1] 190 188 178 150 183

#取出資料
id[2]

## [1] "002"

name[3:5]

## [1] "spiderman"   "wolverine"   "wonderwoman"

name[-1]

## [1] "batman"      "spiderman"   "wolverine"   "wonderwoman"

name[-c(1,3,5)]

## [1] "batman"    "wolverine"

#將這些向量組合為data frame
heroes <- data.frame(id, name, height, weight, gender)
heroes

##    id        name height weight gender
## 1 001    superman    190    102   Male
## 2 002      batman    188     95   Male
## 3 003   spiderman    178     76   Male
## 4 004   wolverine    150     88   Male
## 5 005 wonderwoman    183     59 Female

#用class()查詢資料型態
class(heroes)

## [1] "data.frame"

class(name)

## [1] "character"

class(height)

## [1] "numeric"

class(gender)

## [1] "character"

#存成.RData格式
save(heroes, file = "heroes.RData")
load("heroes.RData")

#取出資料
heroes[2, ]#取出第二列資料

##    id   name height weight gender
## 2 002 batman    188     95   Male

heroes[,2]#取出第二欄資料

## [1] superman    batman      spiderman   wolverine   wonderwoman
## Levels: batman spiderman superman wolverine wonderwoman

heroes[2, 2]##取出第二列第二欄資料

## [1] batman
## Levels: batman spiderman superman wolverine wonderwoman

heroes[5,]

##    id        name height weight gender
## 5 005 wonderwoman    183     59 Female

#用欄位名稱取出某欄的資料，有兩種方法：
heroes[["name"]]

## [1] superman    batman      spiderman   wolverine   wonderwoman
## Levels: batman spiderman superman wolverine wonderwoman

##或是
heroes$name

## [1] superman    batman      spiderman   wolverine   wonderwoman
## Levels: batman spiderman superman wolverine wonderwoman

heroes$height

## [1] 190 188 178 150 183

mean(heroes$height)

## [1] 177.8

heroes[1:3,]

##    id      name height weight gender
## 1 001  superman    190    102   Male
## 2 002    batman    188     95   Male
## 3 003 spiderman    178     76   Male

heroes[heroes$name=="spiderman",]

##    id      name height weight gender
## 3 003 spiderman    178     76   Male

heroes[heroes$name!="spiderman",]

##    id        name height weight gender
## 1 001    superman    190    102   Male
## 2 002      batman    188     95   Male
## 4 004   wolverine    150     88   Male
## 5 005 wonderwoman    183     59 Female

heroes[heroes$height>180,]

##    id        name height weight gender
## 1 001    superman    190    102   Male
## 2 002      batman    188     95   Male
## 5 005 wonderwoman    183     59 Female

barplot(sort(heroes$height, decreasing = TRUE), main = "Heroes", sub = "by Peter Liu", names.arg = heroes$name, xlab = "name", ylab = "height", col = c(1:5))