calculate row sum and product in data.frame - r

Question

I would like to append a columns to my data.frame in R that contain row sums and products
Consider following data frame
x y z
1 2 3
2 3 4
5 1 2
I want to get the following
x y z sum prod
1 2 3 6 6
2 3 4 9 24
5 1 2 8 10
I have tried
sum = apply(ages,1,add)
but it gives me a row vector. Can some one please show me an efficient command to sum and product and append them to original data frame as shown above?

Answer 1

Try
transform(df, sum=rowSums(df), prod=x*y*z)
# x y z sum prod
#1 1 2 3 6 6
#2 2 3 4 9 24
#3 5 1 2 8 10
Or
transform(df, sum=rowSums(df), prod=Reduce(`*`, df))
# x y z sum prod
#1 1 2 3 6 6
#2 2 3 4 9 24
#3 5 1 2 8 10
Another option would be to use rowProds from matrixStats
library(matrixStats)
transform(df, sum=rowSums(df), prod=rowProds(as.matrix(df)))
If you are using apply
df[,c('sum', 'prod')] <- t(apply(df, 1, FUN=function(x) c(sum(x), prod(x))))
df
# x y z sum prod
#1 1 2 3 6 6
#2 2 3 4 9 24
#3 5 1 2 8 10

Answer 2

Another approach.
require(data.table)
# Create data
dt <- data.table(x = c(1,2,5), y = c(2,3,1), z = c(3,4,2))
# Create index
dt[, i := .I]
# Compute sum and prod
dt[, sum := sum(x, y, z), by = i]
dt[, prod := prod(x, y, z), by = i]
dt
# Compute sum and prod using .SD
dt[, c("sum", "prod") := NULL]
dt
dt[, sum := sum(.SD), by = i, .SDcols = c("x", "y", "z")]
dt[, prod := prod(.SD), by = i, .SDcols = c("x", "y", "z")]
dt
# Compute sum and prod using .SD and list
dt[, c("sum", "prod") := NULL]
dt
dt[, c("sum", "prod") := list(sum(.SD), prod(.SD)), by = i,
.SDcols = c("x", "y", "z")]
dt
# Compute sum and prod using .SD and lapply
dt[, c("sum", "prod") := NULL]
dt
dt[, c("sum", "prod") := lapply(list(sum, prod), do.call, .SD), by = i,
.SDcols = c("x", "y", "z")]
dt

Answer 3

Following can also be done but column names need to be entered:
ddf$sum = with(ddf, x+y+z)
ddf$prod = with(ddf, x*y*z)
ddf
x y z sum prod
1 1 2 3 6 6
2 2 3 4 9 24
3 5 1 2 8 10
With data.table, another form can be:
library(data.table)
cbind(dt, dt[,list(sum=x+y+z, product=x*y*z),])
x y z sum product
1: 1 2 3 6 6
2: 2 3 4 9 24
3: 5 1 2 8 10
A simpler version is suggested by #David Arenberg in comments:
dt[, ":="(sum = x+y+z, product = x*y*z)]

Answer 4

Only a partial answer, but if all values are greater than or equal to 0, rowSums/rowsum can be used to calculate products:
df <- data.frame(x = c(1, 2, 5), y = c(2, 3, 1), z = c(3, 4, 2))
# custom row-product-function
my_rowprod <- function(x) exp(rowSums(log(x)))
df$prod <- my_rowprod(df)
df
The generic version is (including negatives):
my_rowprod_2 <- function(x) {
sign <- ifelse((rowSums(x < 0) %% 2) == 1, -1, 1)
prod <- exp(rowSums(log(abs(x)))) * sign
prod
}
df$prod <- my_rowprod_2(df)
df