Access variable value where the name of variable i

问题:

Similar questions have been raised for other languages: C, sql, java, etc.

But I'm trying to do this in R.

I have:

ret_series <- c(1, 2, 3)
x <- "ret_series"

How do I get (1, 2, 3) by calling some function / manipulation on x, without direct mentioning of ret_series?

回答1:

You provided the answer in your question. Try get.

> get(x)
[1] 1 2 3

回答2:

For a one off use, the get function works (as has been mentioned), but it does not scale well to larger projects. it is better to store you data in lists or environments, then use [[ to access the individual elements:

mydata <- list( ret_series=c(1,2,3) )
x <- 'ret_series'

mydata[[x]]

回答3:

What's wrong with either of the following?

eval(as.name(x))

eval(as.symbol(x))

回答4:

Note that some of the examples above wouldn't work for a data.frame.

For instance, given

x <- data.frame(a=seq(1,5))

get("x$a") would not give you x$a.