使用列号对data.table对象的列进行排序很容易，但是使用列名进行排序却有所不同。如果列名称存储在向量中，并且我们希望data.table使用该名称以升序对对象列进行排序，则将在单方括号和双方括号中使用order函数，如以下示例所示。
加载data.table包并创建一个data.table对象-
library(data.table) x1<-rpois(20,1) x2<-rpois(20,5) DT1<-data.table(x1,x2) DT1输出结果
x1 x2 1: 1 3 2: 1 6 3: 2 3 4: 0 7 5: 1 8 6: 0 5 7: 1 3 8: 0 4 9: 1 2 10: 0 6 11: 0 5 12: 0 4 13: 2 6 14: 0 6 15: 2 0 16: 0 2 17: 1 6 18: 0 6 19: 2 7 20: 2 2
Column_for_sorting <-“ x2”
使用Column_for_sorting对DT1进行排序-
DT1[order(DT1[[Column_for_sorting]])]输出结果
x1 x2 1: 2 0 2: 1 2 3: 0 2 4: 2 2 5: 1 3 6: 2 3 7: 1 3 8: 0 4 9: 0 4 10: 0 5 11: 0 5 12: 1 6 13: 0 6 14: 2 6 15: 0 6 16: 1 6 17: 0 6 18: 0 7 19: 2 7 20: 1 8
y1<-rnorm(20) y2<-rnorm(20) DT2<-data.table(y1,y2) DT2输出结果
y1 y2 1: 0.3499126 1.6988660 2: -0.6970935 -1.2961417 3: 0.1244235 1.1192189 4: -1.0639993 0.2504188 5: -0.5714189 0.9772097 6: 1.3096543 1.5397439 7: 0.1163726 -2.8518334 8: -1.2941302 0.6353213 9: -0.4853220 -0.2274419 10: -0.3999413 -0.4259027 11: 2.9027999 0.2589249 12: 1.6724920 -1.2572220 13: 0.8792422 -0.5715381 14: 1.3257716 1.4083895 15: -0.9301681 0.1565980 16: -1.3777834 0.3630332 17: 0.1585897 -1.7692727 18: -2.7972968 -0.3854796 19: -1.4035229 -0.9016175 20: 1.4411729 0.1969444
Column_for_sorting <-“ y1”
使用Column_for_sorting对DT2进行排序-
DT2[order(DT2[[Column_for_sorting]])]输出结果
y1 y2 1: -2.7972968 -0.3854796 2: -1.4035229 -0.9016175 3: -1.3777834 0.3630332 4: -1.2941302 0.6353213 5: -1.0639993 0.2504188 6: -0.9301681 0.1565980 7: -0.6970935 -1.2961417 8: -0.5714189 0.9772097 9: -0.4853220 -0.2274419 10: -0.3999413 -0.4259027 11: 0.1163726 -2.8518334 12: 0.1244235 1.1192189 13: 0.1585897 -1.7692727 14: 0.3499126 1.6988660 15: 0.8792422 -0.5715381 16: 1.3096543 1.5397439 17: 1.3257716 1.4083895 18: 1.4411729 0.1969444 19: 1.6724920 -1.2572220 20: 2.9027999 0.2589249