## dplyr 데이터 전처리 작업에 가장 많이 사용되는 패키지


install.packages("dplyr")
library(dplyr)


exam<-read.csv("C:/Users/Admin/Desktop/study/csv_exam.csv")
exam

View(exam)

exam %>% filter(class == 1)

exam %>% filter(class==2)

exam %>% filter(class!=1)

exam %>% filter(english <= 80)

exam %>% filter(class ==2 & math >= 60)

exam %>% filter(science < 50 | english < 90)

exam %>% filter(class == 1 | class == 3 | class == 5)

class1<-exam %>% filter(class==1)
class1

class2<-exam %>% filter(class==2)
class2

mean(class1$math)
mean(class2$science)

class5<-exam %>% filter(class==5)
mean(class5$math)

class3<-exam %>% filter(class==3)
mean(class3$english)


install.packages("ggplot2")
library(ggplot2)

mpg<-as.data.frame(ggplot2::mpg)

View(mpg)

m1<-mpg %>% filter(displ <= 4)
m2<-mpg %>% filter(displ >= 5)

mm1<-mean(m1$hwy)
mm2<-mean(m2$hwy)

mm1
mm2

ifelse(mm1>mm2, mm1, mm2)

audi<-mpg %>%filter(manufacturer == "audi")
audi
audi_mean_cty<-mean(audi$cty)
audi_mean_cty

toyota<-mpg %>%filter(manufacturer == "toyota")
toyota
toyota_mean_cty<-mean(toyota$cty)
toyota_mean_cty


exam %>% select(class, math, english)

exam %>% select(-math)

exam %>% filter(class==1) %>% select(english)
exam %>% filter(class==2) %>% select(math)

exam %>%
  filter(class==1) %>%
  select(english)

qq<-exam %>%
  filter(class==2) %>%
  select(math)

qq

mean(qq$math)


exam %>%
  filter(class==1) %>%
  head(2)















