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How to divide columns of a matrix by vector elements in R?
Suppose we have a vector say V that contains five elements and a matrix say M that has five columns. Now again, suppose that we want to divide each column in M by corresponding value in vector V, which means first column in M will be divided by first value in the V and so on then we can use the sweep function as shown below −
sweep(M,2,V,FUN="/")
Example 1
Consider the below matrix and vector −
M1<-matrix(rpois(80,10),ncol=4) M1
The following dataframe is created
[,1] [,2] [,3] [,4] [1,] 9 15 10 12 [2,] 9 11 10 10 [3,] 9 11 11 4 [4,] 10 13 11 10 [5,] 9 12 7 7 [6,] 8 9 9 16 [7,] 7 9 12 8 [8,] 12 7 13 11 [9,] 16 8 10 6 [10,] 12 10 7 9 [11,] 14 9 12 10 [12,] 10 8 5 11 [13,] 8 13 8 10 [14,] 8 5 7 8 [15,] 10 14 8 13 [16,] 7 10 9 7 [17,] 11 9 10 12 [18,] 15 11 17 8 [19,] 6 16 14 14 [20,] 12 6 13 8
To divide columns of M1 with corresponding values in V1 on the above created data frame, add the following code to the above snippet −
M1<-matrix(rpois(80,10),ncol=4) V1<-1:4 sweep(M1,2,V1,FUN="/")
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[,1] [,2] [,3] [,4] [1,] 9 7.5 3.333333 3.00 [2,] 9 5.5 3.333333 2.50 [3,] 9 5.5 3.666667 1.00 [4,] 10 6.5 3.666667 2.50 [5,] 9 6.0 2.333333 1.75 [6,] 8 4.5 3.000000 4.00 [7,] 7 4.5 4.000000 2.00 [8,] 12 3.5 4.333333 2.75 [9,] 16 4.0 3.333333 1.50 [10,] 12 5.0 2.333333 2.25 [11,] 14 4.5 4.000000 2.50 [12,] 10 4.0 1.666667 2.75 [13,] 8 6.5 2.666667 2.50 [14,] 8 2.5 2.333333 2.00 [15,] 10 7.0 2.666667 3.25 [16,] 7 5.0 3.000000 1.75 [17,] 11 4.5 3.333333 3.00 [18,] 15 5.5 5.666667 2.00 [19,] 6 8.0 4.666667 3.50 [20,] 12 3.0 4.333333 2.00
Example 2
Consider the matrix given below −
M2<-matrix(round(rnorm(40),2),ncol=2) M2
The following dataframe is created
[,1] [,2] [1,] 0.91 -0.03 [2,] -0.49 -0.23 [3,] -0.26 0.10 [4,] -0.05 -1.16 [5,] 0.86 -2.16 [6,] 0.58 -0.62 [7,] 0.86 -0.67 [8,] 0.32 -0.54 [9,] 0.90 -0.05 [10,] 0.72 -0.88 [11,] -0.46 -1.61 [12,] 0.02 -0.39 [13,] 1.09 -0.09 [14,] -0.67 0.64 [15,] -1.85 -1.31 [16,] -3.32 -1.12 [17,] 1.39 0.08 [18,] -1.25 -0.55 [19,] 0.50 0.93 [20,] 1.02 -1.29
To divide the columns of M2 with corresponding values in V2 on the above created data frame, add the following code to the above snippet −
M2<-matrix(round(rnorm(40),2),ncol=2) V2<-c(0.5,0.10) sweep(M2,2,V2,FUN="/")
Output
If you execute all the above given snippets as a single program, it generates the following Output −
[,1] [,2] [1,] 1.82 -0.3 [2,] -0.98 -2.3 [3,] -0.52 1.0 [4,] -0.10 -11.6 [5,] 1.72 -21.6 [6,] 1.16 -6.2 [7,] 1.72 -6.7 [8,] 0.64 -5.4 [9,] 1.80 -0.5 [10,] 1.44 -8.8 [11,] -0.92 -16.1 [12,] 0.04 -3.9 [13,] 2.18 -0.9 [14,] -1.34 6.4 [15,] -3.70 -13.1 [16,] -6.64 -11.2 [17,] 2.78 0.8 [18,] -2.50 -5.5 [19,] 1.00 9.3 [20,] 2.04 -12.9
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