How to address variables with paste0?-CodePudding

Let's say I have vectors x_1, x_2, x_3 and a vector with their names:

 x_1<-1:3
 x_2<-3:5
 x_3<-7:9
 names<-c("x_1", "x_2", "x_3")

Is it possible to address those vectors using another vector with their names ? For example:

 for (i in 1:length(names)) {
 print(paste0("x_",i)/2)
}

The example doesn't work, but that's what I'd like to do. Is there any function like "as.name" or whatever that converts paste0 output into a variable name ? Thank you!

CodePudding user response：

We may get the values of all the objects in names (it is better to use a different name as names is a base R function name) in a list with mget, divide by 2 and assign (%=% back to the names)

library(collapse)
names %=%  lapply(mget(names), `/`, 2)

-output

> x_1
[1] 0.5 1.0 1.5
> x_2
[1] 1.5 2.0 2.5
> x_3
[1] 3.5 4.0 4.5

In the base R for loop, we can use assign

for (i in seq_along(names)) {
 assign(paste0("x_",i), get(paste0("x_", i))/2)
}

-checking

> x_1
[1] 0.5 1.0 1.5
> x_2
[1] 1.5 2.0 2.5
> x_3
[1] 3.5 4.0 4.5

CodePudding user response：

You can try a named list?

tibble::lst(x_1, x_2, x_3)[[names[1]]]

Then you can loop

for(i in names){
  print(tibble::lst(x_1, x_2, x_3)[[i]])
}

CodePudding user response：

I think you are looking for the eval(parse(text=...)) combination:

for (i in 1:length(names)) {
  print(eval(parse(text=paste0("x_", i)))/2)
}

gives

[1] 0.5 1.0 1.5
[1] 1.5 2.0 2.5
[1] 3.5 4.0 4.5