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How to find the absolute maximum of a matrix with sign if it contains negative values in R?
If we have positive as well as negative values in a matrix then the maximum of the matrix will be a positive number but if we want to ignore the sign then a number represented with negative sign can also be the maximum. If we want to get the maximum with its sign then which.max function can be used in R. Check out the below examples to understand how to do it.
Example
M1<-matrix(sample(c(-1,5,-2,7,1),36,replace=TRUE),nrow=6) M1
Output
[,1] [,2] [,3] [,4] [,5] [,6] [1,] 7 5 1 -2 -1 1 [2,] -1 5 -1 -1 7 1 [3,] -2 5 7 1 -2 -2 [4,] 5 -1 5 -1 5 -2 [5,] -1 1 1 -1 -1 -1 [6,] 1 7 -2 1 5 -2
Example
M1[which.max(abs(M1))]
Output
[1] 7
Example
M2<-matrix(round(rnorm(100),0),nrow=10) M2
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [1,] 0 -1 -1 -1 -1 -1 1 -1 1 0 [2,] 1 0 1 0 2 0 2 -1 0 0 [3,] 0 0 0 1 -1 -1 1 0 0 0 [4,] 1 1 -1 0 0 1 -1 2 -1 0 [5,] 1 -1 1 0 0 0 0 1 0 0 [6,] -1 0 1 2 0 -1 0 -1 2 0 [7,] 0 1 -2 -1 -1 0 0 2 0 0 [8,] 1 0 0 0 0 -1 1 0 0 1 [9,] 1 1 -1 -1 1 -3 0 0 2 -1 [10,] 0 0 0 -1 0 1 0 0 0 1
Example
M2[which.max(abs(M2))]
Output
[1] -3
Example
M3<-matrix(round(runif(25,-5,2),0),nrow=5) M3
Output
[,1] [,2] [,3] [,4] [,5] [1,] 1 1 -1 1 -1 [2,] -5 -3 -1 -4 0 [3,] 2 -3 -2 -2 1 [4,] -3 1 -2 -5 -2 [5,] -2 -2 0 -1 -1
Example
> M3[which.max(abs(M3))]
Output
[1] -5
Example
M4<-matrix(round(rnorm(100,1,0.98),0),nrow=10) M4
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [1,] 1 2 1 0 1 1 2 0 0 2 [2,] 1 1 2 3 1 2 2 0 0 1 [3,] 1 0 2 2 -1 1 1 0 1 0 [4,] 0 -1 0 0 0 1 -1 1 2 1 [5,] 0 3 -1 2 1 1 1 2 2 0 [6,] 2 2 1 -1 2 2 -1 -1 1 -1 [7,] 3 1 0 1 0 -1 0 2 -1 1 [8,] 1 2 1 1 0 -1 0 0 2 1 [9,] 2 -1 1 0 2 -1 2 0 1 3 [10,] 2 1 -1 3 0 2 1 0 0 2
Example
M4[which.max(abs(M4))] [1] 3
Example
M5<-matrix(round(rnorm(100,50,41),0),nrow=10) M5
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [1,] -16 57 47 63 79 99 17 42 110 104 [2,] -4 55 51 -22 56 59 42 13 74 53 [3,] 2 53 96 84 94 74 86 90 79 18 [4,] -16 100 33 64 65 132 38 58 50 -8 [5,] 166 75 69 125 41 58 28 88 53 75 [6,] 26 3 25 -36 50 81 19 56 55 51 [7,] 55 -28 64 90 94 63 9 153 82 44 [8,] 100 76 63 48 31 66 65 96 106 111 [9,] 86 93 48 145 97 60 44 78 67 84 [10,] -19 82 0 119 68 28 43 65 24 6
Example
M5[which.max(abs(M5))]
Output
[1] 166
Example
M6<-matrix(sample(c(-10:10),64,replace=TRUE),nrow=8) M6
Output
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [1,] 9 5 -9 6 -1 6 -3 -2 [2,] 5 -1 -1 -10 -5 6 8 -7 [3,] 9 7 1 5 8 4 3 -7 [4,] -2 5 -2 6 0 -1 -9 2 [5,] 10 1 2 9 1 2 2 6 [6,] 8 -3 10 4 -4 2 -6 3 [7,] -1 3 0 8 4 -5 -9 -10 [8,] -9 -8 3 -6 -8 -6 6 -7
Example
M6[which.max(abs(M6))]
Output
[1] 10
Updated on: 05-Dec-2020
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