R matrix is a two dimensional array. R has a lot of operator and functions that make matrix handling very convenient.
>A <- matrix(c(3,5,7,1,9,4),nrow=3,ncol=2,byrow=TRUE) >A
[,1] [,2] [1,] 3 5 [2,] 7 1 [3,] 9 4
Matrix row and column count:
>rA <- nrow(A) >rA
>cA <- ncol(A) >cA
t(A)function returns a transposed matrix of A:
>B <- t(A) >B
[,1] [,2] [,3] [1,] 3 7 9 [2,] 5 1 4
C <- A * A C
[,1] [,2] [1,] 9 25 [2,] 49 1 [3,] 81 16
>C <- A + A >C
[,1] [,2] [1,] 6 10 [2,] 14 2 [3,] 18 8
Matrix subtraction (-) and division (/) operations ... ...
Sometimes a matrix need to be sorted by a specific column, which can be done by using
Following is a csv file example.
Following R code will read in the above file into a matrix, and sort it by column 4, then write to a output file.
The result is:
Download the csv file and the R source code:
R Source Code File
Order() returns a permutation which rearranges its first argument
into ascending or descending order, breaking ties by further
order(..., na.last = TRUE, decreasing = FALSE)
...: a sequence of numeric, complex, character or logical vectors, all of the same length, or a classed R object.
decreasing: logical. Should the sort order be increasing or decreasing?
na.last: for controlling the treatment of 'NA's. If 'TRUE', missing values in the data are put last; if 'FALSE', they are put first; if 'NA', they are removed.