r - 向量化 R 中的哪些语句

Question

我目前有以下代码。

names <- c("Red","Green","Blue","Orange","Yellow")
aMatrix <- matrix(data=0,nrow=5,ncol=5)
df <- data.frame(matrix(nrow=5,ncol=2))
colnames(df)=c("Number","name")    
selectedRows=sample(1:5, 5)
samples=sample(1:5, 5)
for (i in 1:5){
    df[i,"Number"]=i
    df[i,"name"]=names[samples[i]]
}
for (i in 1:5){
    aMatrix[i,which(names==df[selectedRows[i],"name"])]=1
}

有没有办法对最后一个循环进行矢量化，使其运行得更快？

Answer 1

可以通过使用 match 创建列索引，cbind 行索引与列索引来从 aMatrix 中提取值来完成并将它们分配给 1

aMatrix2 <- aMatrix # before the assignment in OP's code
aMatrix2[cbind(seq_len(nrow(aMatrix)), match(df$name[selectedRows], names))] <- 1

-检查

identical(aMatrix, aMatrix2)
#[1] TRUE