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Find the column number with largest value for each row in an R matrix.
To check which column has the largest value for each row in an R matrix, we can use apply function.
For Example, if we have a matrix called M then we can find column that has the largest value for each row by using the command given below −
apply(M,1,which.max)
Example 1
Consider the matrix given below −
M1<-matrix(rpois(80,10),ncol=4) M1
The following dataframe is created
[,1] [,2] [,3] [,4] [1,] 7 9 14 8 [2,] 13 11 14 11 [3,] 10 17 15 18 [4,] 12 4 11 9 [5,] 15 9 15 10 [6,] 8 13 6 16 [7,] 12 8 11 10 [8,] 11 9 12 17 [9,] 12 7 6 3 [10,] 8 11 12 9 [11,] 6 9 9 8 [12,] 15 10 6 6 [13,] 8 4 8 12 [14,] 13 9 11 6 [15,] 12 11 8 9 [16,] 17 8 6 18 [17,] 6 11 8 7 [18,] 11 13 10 8 [19,] 9 11 7 17 [20,] 8 13 13 17
To find the column number that has largest value for each row in M1 on the above created data frame, add the following code to the above snippet −
M1<-matrix(rpois(80,10),ncol=4) apply(M1,1,which.max)
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 3 3 4 1 1 4 1 4 1 3 2 1 4 1 1 4 2 2 4 4
Example 2
Consider the matrix given below −
M2<-matrix(round(rnorm(60),2),ncol=3) M2
The following dataframe is created
[,1] [,2] [,3] [1,] 0.88 -1.37 0.95 [2,] -1.05 1.53 -0.84 [3,] -1.17 -0.35 -0.05 [4,] -0.54 -0.54 -2.06 [5,] -0.91 -1.02 -0.09 [6,] -0.24 -0.05 -0.14 [7,] 0.13 0.01 0.99 [8,] 0.31 -0.36 0.34 [9,] -0.31 1.34 -1.62 [10,] 0.22 1.75 1.15 [11,] 0.21 -0.77 -1.02 [12,] -2.85 1.91 0.30 [13,] -0.67 -0.17 -1.01 [14,] -1.58 -0.11 -1.36 [15,] 0.33 1.28 -0.04 [16,] -0.63 0.26 1.53 [17,] 0.39 -0.14 0.23 [18,] 1.10 -1.43 0.46 [19,] 1.56 -0.46 -1.09 [20,] -0.15 0.83 0.48
To find the column number that has largest value for each row in M2 on the above created data frame, add the following code to the above snippet −
M2<-matrix(round(rnorm(60),2),ncol=3) apply(M2,1,which.max)
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 3 2 3 1 3 2 3 3 2 2 1 2 2 2 2 3 1 1 1 2
Example 3
Consider the matrix given below −
M3<-matrix(round(rexp(60,1),1),ncol=3) M3
The following dataframe is created
[,1] [,2] [,3] [1,] 0.8 0.7 0.1 [2,] 0.2 0.4 0.4 [3,] 0.9 0.0 0.3 [4,] 0.8 0.4 0.2 [5,] 2.5 4.2 1.1 [6,] 3.6 0.9 0.0 [7,] 0.2 0.0 1.1 [8,] 1.4 0.1 0.7 [9,] 0.5 2.0 0.3 [10,] 1.6 0.0 0.3 [11,] 0.6 0.0 2.3 [12,] 1.3 0.0 0.9 [13,] 1.1 0.7 1.5 [14,] 0.5 0.2 2.3 [15,] 0.5 0.7 0.5 [16,] 0.0 1.1 2.3 [17,] 0.2 0.5 0.1 [18,] 0.8 0.1 1.5 [19,] 2.2 0.6 0.1 [20,] 1.1 0.6 0.7
To find the column number that has largest value for each row in M3 on the above created data frame, add the following code to the above snippet −
M3<-matrix(round(rexp(60,1),1),ncol=3) apply(M3,1,which.max)
If you execute all the above given snippets as a single program, it generates the following Output −
[1] 1 2 1 1 2 1 3 1 2 1 3 1 3 3 2 3 2 3 1 1
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