基于逐列变化的列索引从矩阵中提取矢量

I am struggling with a theoretically simple problem with R:

我正在努力解决R的一个理论上简单的问题：

say I have the following matrix:

说我有以下矩阵：

a <- matrix(1:16,ncol=4)

and the following vector showing the column position I need to extract for each row:

以下向量显示我需要为每行提取的列位置：

b <- c(4,3,1,1)

I need to return the following vector:

我需要返回以下向量：

[1] 13 10  3  4

In other words, for each row I need to extract the element whose column position is shown in the corrisponding c value.

换句话说，对于每一行，我需要提取其列位置显示在相应c值中的元素。

I have search extensively on this site but could not find a solution.

我在这个网站上广泛搜索但找不到解决方案。

Can anyone please help me? Thanks

谁能帮帮我吗？谢谢

1 个解决方案

#1

You can try

你可以试试

 a[cbind(1:nrow(a), b)]
 #[1] 13 10  3  4