r - 向量化 R 中的二维函数

Question

我有一些真实的和预测的标签

truth <- factor(c("+","+","-","+","+","-","-","-","-","-"))
pred  <- factor(c("+","+","-","-","+","+","-","-","+","-"))

我想构建混淆矩阵。我有一个适用于一元元素的函数

f <- function(x,y){ sum(y==pred[truth == x])}

但是，当我将它应用于外积以构建矩阵时，R 似乎不高兴。

outer(levels(truth), levels(truth), f)
Error in outer(levels(x), levels(x), f) : 
  dims [product 4] do not match the length of object [1]

在 R 中为此推荐的策略是什么？

我总是可以通过更高阶的东西，但这看起来很笨拙。

Answer 1

我有时也无法理解 outer 哪里出错了。对于这个任务，我会使用表函数:

> table(truth,pred)   # arguably a lot less clumsy than your effort.
     pred
truth - +
    - 4 2
    + 1 3

在这种情况下，您要测试多值向量是否为标量的“==”。