How to combine two rows in data.table object in R by addition?

To combine two rows in data.table object in R by addition, we can follow the below steps −

• First of all, create a data.table object.

• Then, using plus sign (+) to add two rows and store the addition in one of the rows.

• After that, remove the row that is not required by subsetting with single square brackets.

Example

Create the data.table object

Let’s create a data.table object as shown below: −

library(data.table)
x<-sample(1:5,25,replace=TRUE)
y<-sample(1:5,25,replace=TRUE)
z<-sample(1:5,25,replace=TRUE)
DT<-data.table(x,y,z)
DT

Output

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

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

Add two rows

Using plus sign to add row 1 and row 2 then storing the sum in row 1 −

library(data.table)
x<-sample(1:5,25,replace=TRUE)
y<-sample(1:5,25,replace=TRUE)
z<-sample(1:5,25,replace=TRUE)
DT<-data.table(x,y,z)
DT[1,]<-DT[1,]+DT[2,]
DT

Output

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

Remove the row which is not required

Using single square subsetting to remove 2^nd row from data.table object DT −

library(data.table)
x<-sample(1:5,25,replace=TRUE)
y<-sample(1:5,25,replace=TRUE)
z<-sample(1:5,25,replace=TRUE)
DT<-data.table(x,y,z)
DT[1,]<-DT[1,]+DT[2,]
DT[-2,]

Output

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