r - 将数据框的列相乘

Question

我一直为此而挠头。我有两个数据框:df

df <- data.frame(group = 1:3,
                 age = seq(30, 50, length.out = 3),
                 income = seq(100, 500, length.out = 3),
                 assets = seq(500, 800, length.out = 3))

和 weights

weights <- data.frame(age = 5, income = 10)

我只想为相同的列名将这两个数据框相乘。我试过这样的事情:

colwise(function(x) {x * weights[names(x)]})(df)

但这显然不起作用 colwise不会在函数内保留列名。我看了各种 mapply解决方案( example )，但我无法想出答案。

由此产生的 data.frame应该是这样的:

structure(list(group = 1:3, age = c(150, 200, 250), income = c(1000, 
3000, 5000), assets = c(500, 650, 800)), .Names = c("group", 
"age", "income", "assets"), row.names = c(NA, -3L), class = "data.frame")

  group age income assets
1     1 150   1000    500
2     2 200   3000    650
3     3 250   5000    800

Answer 1

sweep()是你的 friend ，对于这个特定的例子。它依赖于 df 中的名称和 weights顺序正确，但可以安排。

> nams <- names(weights)
> df[, nams] <- sweep(df[, nams], 2, unlist(weights), "*")
> df
  group age income assets
1     1 150   1000    500
2     2 200   3000    650
3     3 250   5000    800

如果变量名在 weights和 df顺序不同，您可以将它们设置为:

> df2 <- data.frame(group = 1:3,
+                   age = seq(30, 50, length.out = 3),
+                   income = seq(100, 500, length.out = 3),
+                   assets = seq(500, 800, length.out = 3))
> nams <- c("age", "income") ## order in df2
> weights2 <- weights[, rev(nams)]
> weights2  ## wrong order compared to df2
  income age
1     10   5
> df2[, nams] <- sweep(df2[, nams], 2, unlist(weights2[, nams]), "*")
> df2
  group age income assets
1     1 150   1000    500
2     2 200   3000    650
3     3 250   5000    800

换句话说，我们重新排序所有对象，以便 age和 income顺序正确。