calculate row sum and product in data.frame

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             


        

Answer 1

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