r - R中的赋值

Question

如何提高以下代码的速度？

for (i in 1:nrow(training)){
     score[training[i,1],training[i,2],training[i,4]] = training[i,3] 
  }

Training是一个有四列的矩阵。我只想建立一个数组，其值是training[i,3]根据上面的公式。

谢谢！

Answer 1

您可以使用矩阵进行索引。以下是['s 文档的相关部分：

A third form of indexing is via a numeric matrix with the one
 column for each dimension: each row of the index matrix then
 selects a single element of the array, and the result is a vector.

因此，在您的情况下，for可以将循环替换为：

score[training[, c(1, 2, 4)]] <- training[, 3]