[R] Matrix manipulation

[yoooooo]

Hi, let's say I have this

A = matrix(c(1, 2, 4), nrow=1)
colnames(A)=c("YOO1", "YOO2", "YOO3")

# ie
#      YOO1 YOO2 YOO3
#[1,]    1    2    4

HELLO <- NULL
HELLO$YOO1="BOO"
HELLO$YOO2="BOO"
HELLO$YOO3="HOO"

and I want a matrix that will sum my categorization.. how can I do it
efficiently without any loop?

#ie   BOO   HOO
#[1,]  3         4

Thanks a lot!
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