order() function sorts a vector, matrix or data frame.

order(x, decreasing = FALSE, na.last = NA, ...)

x: vector
decreasing: decrease or not
na.last: if TRUE, NAs are put at last position, FALSE at first, if NA, remove them (default)

It sorts vector by its index:

>x <- c(1,2.3,2,3,4,8,12,43,-4,-1,NA)
>order(x)

[1]  9 10  1  3  2  4  5  6  7  8 11

>order(x,decreasing=TRUE)

[1]  8  7  6  5  4  2  3  1 10  9 11

>order(x,decreasing=TRUE, na.last=TRUE)

[1]  8  7  6  5  4  2  3  1 10  9 11

>order(x,decreasing=TRUE, na.last=FALSE)

[1] 11  8  7  6  5  4  2  3  1 10  9

>x <- c(1,2.3,2,3,4,8,12,43,-4,-1,NA)
>sort(x)

[1] -4.0 -1.0 1.0 2.0 2.3 3.0 4.0 8.0 12.0 43.0

>sort(x,decreasing=TRUE)

[1] 43.0 12.0 8.0 4.0 3.0 2.3 2.0 1.0 -1.0 -4.0

>sort(x,decreasing=TRUE, na.last=TRUE)

[1] 43.0 12.0 8.0 4.0 3.0 2.3 2.0 1.0 -1.0 -4.0 NA

>sort(x,decreasing=TRUE, na.last=FALSE)

[1] NA 43.0 12.0 8.0 4.0 3.0 2.3 2.0 1.0 -1.0 -4.0

Sort Matrix by one column, following is a csv file example.

,t1,t2,t3,t4,t5,t6,t7,t8 r1,1,0,1,0,0,1,0,2 r2,1,2,5,1,2,1,2,1 r3,0,0,9,2,1,1,0,1 r4,0,0,2,1,2,0,0,0 r5,0,2,15,1,1,0,0,0 r6,2,2,3,1,1,1,0,0 r7,2,2,3,1,1,1,0,1

>x <- read.csv("ordermatrix.csv",header=T,sep=",");
>x <- x[order(x[,4]),];
>x

"X","t1","t2","t3","t4","t5","t6","t7","t8" "1","r1",1,0,1,0,0,1,0,2 "4","r4",0,0,2,1,2,0,0,0 "6","r6",2,2,3,1,1,1,0,0 "7","r7",2,2,3,1,1,1,0,1 "2","r2",1,2,5,1,2,1,2,1 "3","r3",0,0,9,2,1,1,0,1 "5","r5",0,2,15,1,1,0,0,0

Order data frame:

>BOD #R built-in dataset, Biochemical Oxygen Demand

Time demand
1 1 8.3
2 2 10.3
3 3 19.0
4 4 16.0
5 5 15.6
6 7 19.8

Sort by "demand" column:

>BOD[with(BOD,order(demand)),]

Time demand
1 1 8.3
2 2 10.3
5 5 15.6
4 4 16.0
3 3 19.0
6 7 19.8