R语言函数使用①

首先构造一个二维数据框

df<- data.frame(x=c("A","B","C"),"2010"=c(1,3,4),"2011"=c(3,5,2),check.names = FALSE)
#1.二维数据→一维数据

df_melt <- reshape2::melt(df,id.vars="x",variable.name="year",value.name="value")

df_gather <- tidyr::gather(df,year,value,-x)

#2.一维数据→二维数据

df_dcast <- reshape2::dcast(df_melt,x~year,value.var = "value")

df_spread <- tidyr::spread(df_gather,year,value)

#3.在原有数据框基础添加新列且赋值

df_transform <- transform(df_melt,value2=value*2) 

df_transform2 <- transform(df_melt,value2=ifelse(year=="2011",value*3,value))

df_mutate <- dplyr::mutate(df_melt,value2=ifelse(year=="2011",value*3,value))

#4.排序

df_arrange1 <- dplyr::arrange(df_melt,value)  升序排序

df_arrange2 <- dplyr::arrange(df_melt,desc(value))  降序排序