# Ex 1
df<-data.frame(
  x=rnorm(120,c(0,2,4)),
  y=rnorm(120,c(1,2,1)),
  z=letters[1:3]
)
ggplot(data=df,mapping=aes(x=x,y=y,color=z))+geom_point()+geom_line()
ggplot(data=df,mapping=aes(x=x,y=y))+geom_point()+facet_wrap(~z,3)

#=============================================================================
# Ex 2
scores<-dplyr::data_frame(
  person=rep(c("A","b","c"),each=2),
  time=rep(c("pre","post"),3),
  class1=round(rnorm(6,mean=80,sd=4),0),
  class2=round(jitter(class1,15),0)
)


#=============================================================================
# Ex 3
flights_airlines<-flights %>%
  left_join(airlines,by="carrier")
  
flights_airlines<-flights_airlines %>%
  filter(str_detect(name,"Inc.$"))
flights_airlines<-flights_airlines %>%
  mutate(
    prop_vowels=str_count(flights_airlines$name, "[aeiouAEIOU]")/str_length(flights_airlines$name)
  )
flights_airlines<-flights_airlines %>%
  mutate(vowels_gr=ifelse(prop_vowels>=0.45,1,NA),
         vowels_gr=ifelse(prop_vowels<0.45,2,vowels_gr)
         )
flights_airlines %>%
  group_by(vowels_gr) %>%
  summarise(vowel_count=n())
flights_airlines %>%
  filter(vowels_gr==1) %>%
  group_by(dest) %>%
  summarise(dest_count1=n()) %>%
  arrange(desc(dest_count1)) %>%
  head(7)
flights_airlines %>%
  filter(vowels_gr==2) %>%
  group_by(dest) %>%
  summarise(dest_count2=n()) %>%
  arrange(desc(dest_count2)) %>%
  head(7)


#=============================================================================
# Ex 4
mydata<-flights %>%
  filter(dep_delay<0,arr_delay>0)
mydata1<-mydata %>%
  group_by(dest) %>%
  summarise(dest_num=n(),mean_dist=mean(distance,na.rm = T),mean_arr_delay=mean(arr_delay,na.rm = T))
ggplot(data=mydata1,mapping=aes(x=mean_dist,y=mean_arr_delay))+geom_point()+geom_smooth(method = lm)
flights %>%
  left_join(weather,by=c("origin"="origin","time_hour"="time_hour"))
#=============================================================================
# Ex 5
sign_fun<-function(x,y,a){
  t.test(x,y)
  judge<-ifelse(p_value<a,print("reject H0"),print("fail to reject H0"))
  output<-ifelse(is.character(x)|is.character(y),print("Invalid",judge))
  return(list(p_value,judge,))
}

好难哪啊啊啊啊啊啊

求问+11111111

primes <- function(n){
  p <- 2:n
  i <- 1
  while (p[i] <= sqrt(n)) {
    p <-  p[p %% p[i] != 0 | p==p[i]]
    i <- i+1
  }
  p
}