CODEWITHSUNDEEP
rsum
user3478697
user3478697

Reputation: 253

sum specific columns among rows

I need to sum every two columns for example

x1  x2  x3  x4
12  2   3   7
1   4   6   5

I need 

X1     X2
14     10
5      11

I tried apply function and I tried this function mat is a matrix

mat1=matrix()

for(i in 1:nrow(mat)){
for(j in 1:ncol(mat)){
mat1[i,j]=mat[j,i]+mat[j,i+1]
}}

Upvotes: 3

Views: 721

Answers (3)

agstudy
agstudy

Reputation: 121608

For example: 

 mat[,c(TRUE,FALSE)]+mat[,c(FALSE,TRUE)]

  x1 x3
1 14 10
2  5 11

Upvotes: 2

A5C1D2H2I1M1N2O1R2T1
A5C1D2H2I1M1N2O1R2T1

Reputation: 193687

A generalization of this problem (for a data.frame) might be something like:

sapply(split.default(mydf, 0:(length(mydf)-1) %/% 2), rowSums)
#       0  1
# [1,] 14 10
# [2,]  5 11

Replace the "2" in %/% 2 with the number of sets of columns you would like to "aggregate".

Upvotes: 8

Simon O'Hanlon
Simon O'Hanlon

Reputation: 60000

id <- 1:ncol(mat)
mat[ , id[id%%2!=0] ] + mat[ , id[id%%2==0] ]
     x1 x3
[1,] 14 10
[2,]  5 11

Upvotes: 1

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