Sum columns by group (row names) in a matrix

Question

Let\'s say I have a matrix called x.

x <- structure(c(1, 0, 1, 0, 0, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1), 
.Dim = c(5L, 4L), .Dimname         


        

Answer 1

You can try this

df <- read.table(head=TRUE, text="
Name       Mon   Tue   Wed   Thurs
Cake   1     0     1      1
Pie    0     0     1      1
Cake   1     1     0      1
Pie    0     0     1      1
Pie    0     0     1      1")

aggregate(. ~ Name, data=df, FUN=sum)
##   Name Mon Tue Wed Thurs
## 1 Cake   2   1   1     2
## 2  Pie   0   0   3     3

also with dplyr

library(dplyr)
group_by(df, Name) %>%
    summarise(Mon = sum(Mon), Tue = sum(Tue), Wed = sum(Wed), Thurs = sum(Thurs))

or better

 group_by(df, Name) %>%
    summarise_each(funs(sum))