How to convert data.table object into a matrix in R?

A data.table object is very similar to a data frame in R, therefore, converting a data.table object to a matrix is not a difficult job. We just need to use as.matrix function and store the data.table object into a new object that will belong to the matrix, otherwise R will not be able to convert the data.object to a matrix. For example, if we have a data.table object DT then to convert it into a matrix, we should use the below example code −

DT_matrix<-as.matrix(DT)

Loading data.table package −

library(data.table)

Creating a data.table object −

Example

x1<-rnorm(20,1,0.04) x2<-rnorm(20,5,1.2) x3<-runif(20,5,10) x4<-runif(20,1,5) DT1<-data.table(x1,x2,x3,x4) DT1

Output

x1 x2 x3 x4 1: 0.9785610 7.345365 8.079572 4.289080 2: 0.9787770 6.684993 6.842196 3.420399 3: 0.9936527 5.076511 6.584490 4.339317 4: 0.9585088 6.348905 5.256956 1.041050 5: 1.0172288 6.076759 6.456343 3.964968 6: 1.0199971 6.384019 6.444665 2.477480 7: 1.0027680 5.189908 6.352739 3.358625 8: 1.0013410 7.480771 6.236253 3.704360 9: 0.9638484 3.173219 6.768095 2.710411 10: 0.9771605 4.072879 5.269356 3.689747 11: 0.9768464 3.898211 8.212824 1.230352 12: 1.0322361 4.964122 8.062670 2.333302 13: 0.9730514 2.746493 7.991256 1.319675 14: 1.0157617 4.032643 7.324038 3.883257 15: 1.0167210 6.994750 5.123840 3.157113 16: 0.9526550 5.292459 8.401666 2.362798 17: 1.0022340 4.753125 6.175266 3.900407 18: 1.0456185 6.001135 8.018412 3.324448 19: 1.1422387 5.121760 5.340800 2.348761 20: 0.9269784 5.893736 5.754917 1.940769

is.matrix(DT1_matrix) 

[1] TRUE

Let’s have a look at another example −

Example

y1<-rpois(20,2) y2<-rpois(20,5) y3<-rpois(20,8) y4<-rpois(20,10) y5<-sample(0:9,20,replace=TRUE) DT2<-data.table(y1,y2,y3,y4,y5) DT2

Output

   y1 y2  y3   y4   y5 1: 2  5   12   12   7 2: 2  7   9    8   1 3: 2  5   3    9   2 4: 0  0   10   12   9 5: 2  3   5    8   8 6: 4  7   6   8    9 7: 2  7   8   9    0 8: 0  7   8   11   1 9: 3  6   7   8    2 10: 0  3   8  9    1 11: 2  7  9   9    2 12: 3  4  8   7   7 13: 0  1  10  14 8 14: 1  6  7   5 9 15: 3  3   12 14 6 16: 0  4   8   8 4 17: 1  7   9  13 2 18: 5  1   14  11 7 19: 1 4   14   9 6 20: 3 5   8   10 1

Converting data.table object into a matrix object −

Example

DT2_matrix<-as.matrix(DT2) DT2_matrix

Output

     y1  y2  y3   y4 y5 [1,] 2   5   12   12 7 [2,] 2   7   9   8 1 [3,] 2   5   3   9 2 [4,] 0   0   10 12 9 [5,] 2   3   5 8 8 [6,] 4   7   6 8 9 [7,] 2   7   8 9 0 [8,] 0   7   8 11 1 [9,] 3   6   7 8 2 [10,] 0  3   8 9 1 [11,] 2  7   9 9 2 [12,] 3 4 8 7 7 [13,] 0 1 10 14 8 [14,] 1 6 7 5 9 [15,] 3 3 12 14 6 [16,] 0 4 8 8 4 [17,] 1 7 9 13 2 [18,] 5 1 14 11 7 [19,] 1 4 14 9 6 [20,] 3 5 8 10 1

is.matrix(DT2_matrix) 

[1] TRUE