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How to find the row sum for each column by row name in an R matrix?
To find the row sum for each column by row name, we can use rowsum function. For example, if we have a matrix called M then the row sums for each column with row names can be calculated by using the command rowsum(M,row.names(M)).
Example1
> M1<-matrix(rpois(40,5),nrow=20)
> rownames(M1)<-sample(c("Male","Female"),20,replace=TRUE)
> colnames(M1)<-c("V1","V2")
> M1Output
V1 V2 Male 3 6 Female 6 5 Female 7 3 Female 2 5 Female 5 3 Female 4 4 Female 1 4 Female 4 4 Female 7 5 Male 2 5 Female 5 5 Male 7 1 Female 5 6 Male 6 5 Female 3 7 Male 5 4 Female 3 6 Male 3 4 Male 4 3 Male 6 2
Finding the row sums with column names of matrix M1 −
> rowsum(M1,row.names(M1))
Output
V1 V2 Female 52 57 Male 36 30
Example2
> M2<-matrix(rpois(40,10),nrow=20)
> rownames(M2)<-sample(LETTERS[1:4],20,replace=TRUE)
> colnames(M2)<-c("X1","X2")
> M2Output
X1 X2 B 6 9 D 12 14 C 8 9 A 9 8 A 6 13 A 10 8 D 7 12 B 9 6 A 11 11 C 6 15 D 12 6 B 5 9 C 12 11 A 12 6 B 10 9 D 15 14 C 8 10 B 11 9 A 8 8 B 19 4
Finding the row sums with column names of matrix M2 −
> rowsum(M2,row.names(M2))
Output
X1 X2 A 56 54 B 60 46 C 34 45 D 46 46
Example3
> M3<-matrix(sample(0:9,40,replace=TRUE),nrow=20)
> rownames(M3)<-sample(c("Hot","Cold"),20,replace=TRUE)
> colnames(M3)<-c("C1","C2")
> M3Output
C1 C2 Cold 1 5 Hot 1 3 Hot 4 5 Cold 0 3 Hot 2 8 Hot 7 6 Hot 5 9 Cold 5 9 Cold 9 9 Cold 8 7 Cold 9 2 Cold 0 6 Cold 0 3 Cold 6 3 Cold 3 8 Cold 6 2 Cold 5 0 Cold 4 9 Cold 9 2 Hot 6 5
Finding the row sums with column names of matrix M3 −
> rowsum(M3,row.names(M3))
Output
C1 C2 Cold 65 68 Hot 25 36
Updated on: 05-Mar-2021
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