How to change the sign of even number rows in column of a data.table object in R?

To change the sign of even number rows in a data.table object in R, we can follow the below steps −

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

• Then, use vector multiplication with 1 and minus 1 to change the sign of even number rows.

Example

Create the data.table object

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

library(data.table) x<-sample(-5:5,30,replace=TRUE) DT<-data.table(x) DT

Output

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

 x 1: 2 2: 3 3: 5 4: 2 5: 5 6: -5 7: 2 8: 3 9: 0 10: 3 11: 3 12: -3 13: -1 14: -4 15: 5 16: 5 17: -1 18: -4 19: -5 20: -1 21: 4 22: 5 23: 2 24: 0 25: -3 26: 0 27: -2 28: 1 29: 4 30: -1 x

Change the sign of even number rows

Using vector multiplication with 1 and minus 1 to change the sign of even number rows in column x of data.table object DT −

library(data.table) x<-sample(-5:5,30,replace=TRUE) DT<-data.table(x) DT$x<-DT$x*c(1,-1) DT

Output

 x 1: 2 2: -3 3: 5 4: -2 5: 5 6: 5 7: 2 8: -3 9: 0 10: -3 11: 3 12: 3 13: -1 14: 4 15: 5 16: -5 17: -1 18: 4 19: -5 20: 1 21: 4 22: -5 23: 2 24: 0 25: -3 26: 0 27: -2 28: -1 29: 4 30: 1 x