image.png

library(tidyr)
a <- data.frame(country= c("A","B","C"),"1999"= paste(c(0.7,37,212),"K"),"2000"= paste(c(2,80,213),"K"))
a
#######数据框的变形#######
gather(a,"year","cases",X1999,X2000) 
gather(a,"year","cases",-country)

########跟据一个表格衍生出其他表格#########
expand(a,country,X1999,X2000)

#######处理缺失值#####
A <- data.frame(country= c("A","B","C"),"1999"= c(0.7,NA,212),"2000"= c(2,80,NA))
B <- drop_na(A,X1999)
B
C <- fill(A,X1999)
C