),each = 2), score = c(5,3,-2,-4))df1从文件中读取df2 -是赋值的意思## 代码思维#如何取数据框的最后一列?...df1[,3]df1[,ncol(df1)]#如何取数据框除了最后一列以外的其他列?df1[,-ncol(df1)] 注:!-给数值用,!给逻辑值用。...c("r1","r2","r3","r4")#只修改某一行/列的名colnames(df1)[2] <- "CHANGE"列名和行名都是向量#6.两个数据框的连接test1 <- data.frame(...test <- read.csv("exercise.csv")# 2.求test第一列数值的中位数median(test$Petal.Length)# 3.筛选test中,Species列的值为a或c