数据集中的列从指定行中的最大值到最小值

Question

Suppose I have a dataset:

library(data.table)

dat1<-data.table(id=c(111,111,111,222,222,222), year=c(1995,1996,1997,1995,1996,1997), value=c(4,5,1,2,6,7))

How do I order the columns of the dataset based on the size of the values in row 1 (or an arbitrary row).

I want my output to be:

dat2<-data.table(value=c(4,5,1,2,6,7),id=c(111,111,111,222,222,222), year=c(1995,1996,1997,1995,1996,1997)

Because in dat1 row 1, value 4 is the smallest value making "dat1$value" column 1, id 111 is second smallest value making "dat1$id" column 2 and year 1995 is biggest value making "dat1$year" column 3.

Answer 1

You can do setcolorder

setcolorder(dat1, names(dat1)[order(dat1[1])])
dat1
   value  id year
1:     4 111 1995
2:     5 111 1996
3:     1 111 1997
4:     2 222 1995
5:     6 222 1996
6:     7 222 1997

Method 2

dat1 = dat1[,names(dat1)[order(dat1[1,])],with=F]
   value  id year
1:     4 111 1995
2:     5 111 1996
3:     1 111 1997
4:     2 222 1995
5:     6 222 1996
6:     7 222 1997

Recommend by RonakShah

dat1[, order(dat1[1, ]), with = FALSE]