How to divide data.table object rows by number of columns in R?


To divide the row values by number of columns in R’s data.table object, we can follow the below steps −

  • First of all, create a data.table object.
  • Then, use apply function to divide the data.table object row values by number of columns.

Create the data frame

Let's create a data frame as shown below −

library(data.table)
x<-sample(0:9,25,replace=TRUE)
y<-sample(0:9,25,replace=TRUE)
DT<-data.table(x,y)
DT

On executing, the above script generates the below output(this output will vary on your system due to randomization) −

   x y
1: 4 4
2: 6 4
3: 6 4
4: 8 0
5: 1 6
6: 2 3
7: 8 9
8: 2 3
9: 3 7
10: 1 3
11: 2 9
12: 7 3
13: 1 0
14: 9 8
15: 5 6
16: 5 8
17: 0 0
18: 7 3
19: 6 7
20: 5 0
21: 1 3
22: 6 0
23: 5 8
24: 4 7
25: 1 1
x y

Divide the data.table object row values by number of columns

Using apply function to divide the row values of DT by number of columns −

library(data.table)
x<-sample(0:9,25,replace=TRUE)
y<-sample(0:9,25,replace=TRUE)
DT<-data.table(x,y)
DT_new<-t(apply(DT,1, function(x) x/length(x)))
DT_new

Output

      x   y
[1,] 2.0 2.0
[2,] 3.0 2.0
[3,] 3.0 2.0
[4,] 4.0 0.0
[5,] 0.5 3.0
[6,] 1.0 1.5
[7,] 4.0 4.5
[8,] 1.0 1.5
[9,] 1.5 3.5
[10,] 0.5 1.5
[11,] 1.0 4.5
[12,] 3.5 1.5
[13,] 0.5 0.0
[14,] 4.5 4.0
[15,] 2.5 3.0
[16,] 2.5 4.0
[17,] 0.0 0.0
[18,] 3.5 1.5
[19,] 3.0 3.5
[20,] 2.5 0.0
[21,] 0.5 1.5
[22,] 3.0 0.0
[23,] 2.5 4.0
[24,] 2.0 3.5
[25,] 0.5 0.5

Updated on: 13-Aug-2021

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