How to find the row wise sum for n number of columns in R?

To find the row wise sum of n number of columns can be found by using the rowSums function along with subsetting of the columns with single square brackets.

For example, if we have a data frame called df that contains five columns and we want to find the row sums for last three columns then we can use the following command −

df$Sum_3<-rowSums(df[,3:5])

Example 1

Following snippet creates a sample data frame −

x1<-round(rnorm(20),2) x2<-round(rnorm(20),2) x3<-round(rnorm(20),2) df1<-data.frame(x1,x2,x3) df1

The following dataframe is created −

    x1     x2    x3 1  -0.66  1.01  -0.44 2  -2.05 -0.47   0.42 3   1.11  1.47   1.04 4  -2.55 -0.42  -0.46 5  -0.50 -1.98  -0.41 6  -2.16 -0.34  -0.55 7   0.29 -0.58   0.42 8  -0.67  1.71  -0.86 9  -0.93  0.00   0.00 10  0.30 -0.87   0.27 11  1.27 -1.60  -0.49 12  0.73  1.16  -1.24 13 -0.71  0.20  -1.18 14 -0.31  1.16   0.24 15 -0.76  0.86  -0.70 16  1.11 -0.25  -0.48 17 -0.88 -0.43   0.10 18  0.50 -2.05   0.36 19 -0.30  0.56  -0.97 20 -1.76 -1.39   1.10

To find the row sums for column x2 and x3, add the following code to the above snippet −

x1<-round(rnorm(20),2) x2<-round(rnorm(20),2) x3<-round(rnorm(20),2) df1<-data.frame(x1,x2,x3) df1$Sum_x2_x3<-rowSums(df1[,2:3]) df1

Output

If you execute all the above given snippets as a single program, it generates the following output −

     x1    x2    x3   Sum_x2_x3 1  -0.66  1.01 -0.44  0.57 2  -2.05 -0.47  0.42 -0.05 3   1.11  1.47  1.04  2.51 4  -2.55 -0.42 -0.46 -0.88 5  -0.50 -1.98 -0.41 -2.39 6  -2.16 -0.34 -0.55 -0.89 7   0.29 -0.58  0.42 -0.16 8  -0.67  1.71 -0.86  0.85 9  -0.93  0.00  0.00  0.00 10  0.30 -0.87  0.27 -0.60 11  1.27 -1.60 -0.49 -2.09 12  0.73  1.16 -1.24 -0.08 13 -0.71  0.20 -1.18 -0.98 14 -0.31  1.16  0.24  1.40 15 -0.76  0.86 -0.70  0.16 16  1.11 -0.25 -0.48 -0.73 17 -0.88 -0.43  0.10 -0.33 18  0.50 -2.05  0.36 -1.69 19 -0.30  0.56 -0.97 -0.41 20 -1.76 -1.39  1.10 -0.29

Example 2

Following snippet creates a sample data frame −

y1<-rpois(20,1) y2<-rpois(20,5) y3<-rpois(20,2) y4<-rpois(20,2) df2<-data.frame(y1,y2,y3,y4) df2

The following dataframe is created −

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

To find row sums for column y1 and y2, add the following code to the above snippet −

y1<-rpois(20,1) y2<-rpois(20,5) y3<-rpois(20,2) y4<-rpois(20,2) df2<-data.frame(y1,y2,y3,y4) df2$Sum_y1_y2<-rowSums(df2[,1:2]) df2

Output

If you execute all the above given snippets as a single program, it generates the following output −

   y1 y2 y3 y4 Sum_y1_y2 1  1  6  2  2   7 2  1  4  1  0   5 3  1  6  0  2   7 4  2  9  4  2  11 5  0  7  1  2   7 6  1  5  1  1   6 7  2  0  3  2   2 8  1  2  5  1   3 9  1  6  1  5   7 10 0  3  1  2   3 11 1  4  2  3   5 12 1  7  3  1   8 13 0  8  1  2   8 14 1  5  2  3   6 15 0 10  3  0  10 16 2  2  1  2   4 17 3  5  4  2   8 18 0  6  2  1   6 19 2  2  3  1   4 20 0  6  1  2   6