8. 数据排序
> leadership$age
[1] 32 45 25 39 NA
> newdata <- leadership[order(leadership$age),]
> newdata
manager testDate country gender age item1 item2 item3 item4 item5
3 3 2008-10-01 UK F 25 3 5 5 5 2
1 1 2008-10-24 US M 32 5 4 5 5 5
4 4 2008-10-12 UK M 39 3 3 4 NA NA
2 2 2008-10-28 US F 45 3 5 2 5 5
5 5 2009-05-01 UK F NA 2 2 1 2 1
stringAsFactors agecat
3 FALSE Young
1 FALSE Young
4 FALSE Young
2 FALSE Young
5 FALSE <NA>
>
>
> attach(leadership)
The following objects are masked _by_ .GlobalEnv:
age, country, gender, manager
> newdata <- leadership[order(gender, age),]
> detach(leadership)
> newdata
manager testDate country gender age item1 item2 item3 item4 item5
3 3 2008-10-01 UK F 25 3 5 5 5 2
2 2 2008-10-28 US F 45 3 5 2 5 5
5 5 2009-05-01 UK F NA 2 2 1 2 1
1 1 2008-10-24 US M 32 5 4 5 5 5
4 4 2008-10-12 UK M 39 3 3 4 NA NA
stringAsFactors agecat
3 FALSE Young
2 FALSE Young
5 FALSE <NA>
1 FALSE Young
4 FALSE Young
>
> attach(leadership)
The following objects are masked _by_ .GlobalEnv:
age, country, gender, manager
> newdata <- leadership[order(gender, -age),]
> detach(leadership)
> newdata
manager testDate country gender age item1 item2 item3 item4 item5
5 5 2009-05-01 UK F NA 2 2 1 2 1
2 2 2008-10-28 US F 45 3 5 2 5 5
3 3 2008-10-01 UK F 25 3 5 5 5 2
4 4 2008-10-12 UK M 39 3 3 4 NA NA
1 1 2008-10-24 US M 32 5 4 5 5 5
stringAsFactors agecat
5 FALSE <NA>
2 FALSE Young
3 FALSE Young
4 FALSE Young
1 FALSE Young
>
9. 数据集的合并
9.1 添加列
> patientID <- c(1, 2, 3, 4)
> age <- c(25, 34, 28, 52)
> status <- c("poor", "improved", "excellent", "poor")
> gender <- c("F", "M", "M", "F")
> dataframeA <- data.frame(patientID, gender)
> dataframeA
patientID gender
1 1 F
2 2 M
3 3 M
4 4 F
> dataframeB <- data.frame(patientID, age, status)
> dataframeB
patientID age status
1 1 25 poor
2 2 34 improved
3 3 28 excellent
4 4 52 poor
> total <- merge(dataframeA, dataframeB, by="ID")
Error in fix.by(by.x, x) : ‘by‘ must specify a uniquely valid column
> total <- merge(dataframeA, dataframeB, by="patientID")
> total
patientID gender age status
1 1 F 25 poor
2 2 M 34 improved
3 3 M 28 excellent
4 4 F 52 poor
> total <- merge(dataframeA, dataframeB, by=c("gender", "age"))
Error in fix.by(by.x, x) : ‘by‘ must specify a uniquely valid column
> total <- merge(dataframeA, dataframeB, by=c("patientID", "age"))
Error in fix.by(by.x, x) : ‘by‘ must specify a uniquely valid column
>
> total <- cbind(dataframeA, dataframeB)
> total
patientID gender patientID age status
1 1 F 1 25 poor
2 2 M 2 34 improved
3 3 M 3 28 excellent
4 4 F 4 52 poor
>
9.2 添加行
> total <- rbind(dataframeA, dataframeB) Error in rbind(deparse.level, ...) : numbers of columns of arguments do not match
10. 数据集取子集
10.1 选入（保留）变量
10.2 剔除（丢弃）变量
10.3 选入观测
10.4 subset() 函数
10.5 随机抽样
原文：http://www.cnblogs.com/wnzhong/p/7496188.html