如何使用变量的输出来调用R中的向量

Question

Hi can anyone help with this? I'm trying to call a vector with a variable. For example?

var <- 'apple'
apple <- c(1,2,3)

but now say I have a bunch of vectors like apple and I write a function where I'm just given the var variable. How can I access the apple vector with var ? I tried eval(var) but that does not achieve what I want. Thank you.

Answer 1

use get

get(var)
# [1] 1, 2, 3

Answer 2

或使用eval(parse(text=var)) 。

Answer 3

As @mnel notes, you can use get . However, there is probably a better way to go about this using list s.

If you make a list called say fruit like:

apple <- 1:3
orange <- 4:6
pear <- 7:9

fruit <- list(apple=apple,orange=orange,pear=pear)
#$apple
#[1] 1 2 3
#
#$orange
#[1] 4 5 6
#
#$pear
#[1] 7 8 9

Then you can call the elements of fruit using the names you have in var like so:

var <- "apple"

# get the whole list element named "apple"
fruit[var]
#$apple
#[1] 1 2 3

# get the contents of the list element named "apple"
fruit[[var]]
#[1] 1 2 3

If var had several different fruit names listed, it also works:

var <- c("apple","orange")
fruit[var]
#$apple
#[1] 1 2 3
#
#$orange
#[1] 4 5 6