1 向一个data.frame指定列插入一列新数据
1.1 插入一列到指定位置
y<-1:4
data1 <-data.frame(x1=c(1,3,5,7), x2=c(2,4,6,8),x3=c(11,12,13,14),x4=c(15,16,17,18))
data2<-cbind(data1[,1:2],y,data1[,3:ncol(data1)])
插到data1末尾
data2<-cbind(data1,y)
插到第一列
data2<-cbind(y,data1)
2 向一个data.frame指定行插入一行新数据
2.1 插入一行到指定位置
data1<- data.frame(x1=runif(10),x2= runif(10),x3= runif(10))
row<- c(1, 1, 1)
data2<- rbind(data1[1:5,], row, data1[6:nrow(data1), ])
插入到data1末尾
data2<- rbind(data1, row)
插入到data1第一行
data2<- rbind(row, data1)
3 给data frame设置列名
colnames(data2) <- c('row1','row3','row3')
4 创建一个空的data frame，并制定列名（方法有点挫，目前还没找到其他方式）
4.1 创建一个包含一行的，然后用-1取
emptyDF <- data.frame(row1 = c(NA), row2 = c(NA))
emptyDF <- emptyDF[-1,]
4.2 通过matrix创建data frame
emptyDF <- data.frame(matrix(c(NA), byrow = TRUE,dimnames = list(day = c(),condition = c("outlook","temperature","humidity","wind")), nrow=0, ncol=4))
5 创建一个data frame，并查看
trainSet2 <-data.frame(
size=c("大","小","大","大","小","小"),
weight=c("轻","重","轻","轻","重","轻"),
color=c("红","红","红","绿","红","绿"),
taste=c("good","good","bad","bad","bad","good")
)
size weight color taste
1 大 轻 红 good
2 小 重 红 good
3 大 轻 红 bad
4 大 轻 绿 bad
5 小 重 红 bad
6 小 轻 绿 good
6 查看行名
row.names(trainSet2)
7 查看列名
colnames(trainSet2)
8 数据访问
访问第一行
trainSet2[1,]
访问第一列
trainSet2[,1]
trainSet2$size
trainSet2[[1]]
trainSet2[["size"]]
访问多行，例如1,2行
trainSet2[1:2,]
访问多列，例如1,2列
trainSet2[,1:2]
trainSet2[c("size","weight")]
9 添加新列
trainSet2$newc1 <- c(1,2,3,4,5,6)
trainSet2 <- within(trainSet2,{newc2 <- color})
10 数据查询
10.1 根据条件查询
查询taste为good的所有行
trainSet2[trainSet2$taste == "good",]
查询taste为good的指定行
trainSet2[trainSet2$taste == "good",1]
trainSet2[trainSet2$taste == "good",1:2]
trainSet2[trainSet2$taste == "good",c("size","color")]
也可以用which，跟上面的类似
trainSet2[which(trainSet2$taste == "good"),c("size","color")]
使用subset，会简化查询，可以指定条件，指定选择列
subset(trainSet2,taste == "good" & newc1 < 5,select = c("size","taste"))
11 使用sql查询data frame
对于熟悉sql的是个福音啊
11.1 安装sqldf
install.packages('sqldf')
11.2 引入sqldf
library(sqldf)
11.3 查询示例
result <- sqldf("select * from trainSet2 where size='大'")
11.4 链接合并示例，两个表根据newc1 和 fkey进行链接
trainSet3 <- data.frame(fkey = c(1,2,3,4),newc3=c("a","b","c","d"))
resdult <- merge(trainSet2,trainSet3,by.x = "newc1",by.y = "fkey")
newc1 size weight color taste newc2 newc3
1 1 大 轻 红 good 红 a
2 2 小 重 红 good 红 b
3 3 大 轻 红 bad 红 c
4 4 大 轻 绿 bad 绿 d