从R中的列表中提取元素序列

Question

I am looking for a shorter expression for something like the following:

list(x[[1]],x[[2]],x[[3]],x[[4]])

I tried

list(x[[1:4]])

and

list(x[1:4])

but none of these do what the original expression does.

Answer 1

The simple approach is just:

x[[1:4]]

no need to wrap it in list .

If you need to do something a little more complicated, then lapply can be used as well (overkill for this, but I will show an example anyways in case it helps for other cases):

> x <- list()
> x[[1]] <- lm(Sepal.Length ~ ., data=iris)
> x[[2]] <- lm(Sepal.Width ~ ., data=iris)
> x[[3]] <- lm(Petal.Width ~ ., data=iris)
> x[[4]] <- lm(Petal.Length ~ ., data=iris)
> x[[5]] <- lm(Petal.Length ~ Petal.Width, data=iris)
> 
> test1 <- list(x[[1]], x[[2]], x[[3]], x[[4]])
> test2 <- x[1:4]
> test3 <- lapply(1:4, function(i) x[[i]])
> 
> identical(test1,test2)
[1] TRUE
> identical(test1,test3)
[1] TRUE
>