计算data.frame中的行和和产品

Question

我想在R中的一个包含行总和和产品的data.frame中添加一列.请考虑以下数据框

x    y     z
1    2     3
2    3     4
5    1     2

我想得到以下内容

x    y     z    sum    prod
1    2     3    6       6  
2    3     4    9       24 
5    1     2    8       10

我试过了

 sum = apply(ages,1,add)

但它给了我一个行向量.有人可以给我一个有效的命令来总结和产品,并将它们附加到原始数据框,如上所示？

Answer 1

尝试

 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

要么

 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

另一种选择是使用rowProds由matrixStats

 library(matrixStats)
 transform(df, sum=rowSums(df), prod=rowProds(as.matrix(df)))

如果你正在使用 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

另一种方法。

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