dplyr学习笔记
什么是dplyr？
dplyr是一个非常强大的转换概括行列表格的R包。主要功能：select()：选择符合条件的列；
filter()：过滤行；
arrange()：对行进行重排序；
mutate()：创建新的列；
summarise()：概括表的信息，如最值，均值等；
group_by()：分组函数，采用“split-apply-combine”的概念。
安装dplyr
library(dplyr)
#数据集mtcars
head(mtcars)
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
select()：选择符合条件的列
head(select(mtcars, mpg, carb))
mpg carb
Mazda RX4 21.0 4
Mazda RX4 Wag 21.0 4
Datsun 710 22.8 1
Hornet 4 Drive 21.4 1
Hornet Sportabout 18.7 2
Valiant 18.1 1
#用-除去不要的列
head(select(mtcars, -mpg))
cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 6 225 105 2.76 3.460 20.22 1 0 3 1
#用：选择列的起始范围，从mpg开始，到wt结束
head(select(mtcars, mpg:wt))
mpg cyl disp hp drat wt
Mazda RX4 21.0 6 160 110 3.90 2.620
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875
Datsun 710 22.8 4 108 93 3.85 2.320
Hornet 4 Drive 21.4 6 258 110 3.08 3.215
Hornet Sportabout 18.7 8 360 175 3.15 3.440
Valiant 18.1 6 225 105 2.76 3.460
filter()：过滤行
filter(mtcars, qsec >= 20) mpg cyl disp hp drat wt qsec vs am gear carb 1 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 2 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 3 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4 2 4 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3 1 filter(mtcars, qsec >= 20, carb == 2) mpg cyl disp hp drat wt qsec vs am gear carb 1 24.4 4 146.7 62 3.69 3.19 20.0 1 0 4 2 2 22.8 4 140.8 95 3.92 3.15 22.9 1 0 4 2 filter(mtcars, disp %in% c(108, 225)) mpg cyl disp hp drat wt qsec vs am gear carb 1 22.8 4 108 93 3.85 2.32 18.61 1 1 4 1 2 18.1 6 225 105 2.76 3.46 20.22 1 0 3 1
%>%管道操作
mtcars %>% select(mpg, hp) %>% head
mpg hp
Mazda RX4 21.0 110
Mazda RX4 Wag 21.0 110
Datsun 710 22.8 93
Hornet 4 Drive 21.4 110
Hornet Sportabout 18.7 175
Valiant 18.1 105
arrange()：对行进行重排序
mtcars %>% arrange(mpg) %>% head mpg cyl disp hp drat wt qsec vs am gear carb 1 10.4 8 472 205 2.93 5.250 17.98 0 0 3 4 2 10.4 8 460 215 3.00 5.424 17.82 0 0 3 4 3 13.3 8 350 245 3.73 3.840 15.41 0 0 3 4 4 14.3 8 360 245 3.21 3.570 15.84 0 0 3 4 5 14.7 8 440 230 3.23 5.345 17.42 0 0 3 4 6 15.0 8 301 335 3.54 3.570 14.60 0 1 5 8 mtcars %>% select(mpg, wt, carb) %>% arrange(mpg) %>% head mpg wt carb 1 10.4 5.250 4 2 10.4 5.424 4 3 13.3 3.840 4 4 14.3 3.570 4 5 14.7 5.345 4 6 15.0 3.570 8 mtcars %>% select(mpg, wt, carb) %>% arrange(mpg) %>% filter(wt >= 5) mpg wt carb 1 10.4 5.250 4 2 10.4 5.424 4 3 14.7 5.345 4mutate()：创建新的列
mtcars %>% mutate(mpg_carb = mpg / carb) %>% head mpg cyl disp hp drat wt qsec vs am gear carb mpg_carb 1 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 5.25 2 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 5.25 3 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 22.80 4 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 21.40 5 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 9.35 6 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1 18.10summarise()：概括表的信息
mtcars %>% summarise(avg_mpg = mean(mpg), min_hp = min(hp), total = n()) avg_mpg min_hp total 1 20.09062 52 32group_by()：分组函数
mtcars %>% group_by(carb) %>%summarise(avg_mpg = mean(mpg), min_hp = min(hp), total = n()) Source: local data frame [6 x 4] carb avg_mpg min_hp total 1 1 25.34286 65 7 2 2 22.40000 52 10 3 3 16.30000 180 3 4 4 15.79000 110 10 5 6 19.70000 175 1 6 8 15.00000 335 1
参考资料：
Introduction to dplyr