R help - Jun 2004 - Fw: Evaluating strings as variables

----- Original Message ----- 
From: Robin Gruna 
To: R-help@lists.R-project.org 
Sent: Sunday, June 20, 2004 5:42 PM
Subject: Evaluating strings as variables


Hello,
I have the following problem: I have a list as follows,
> values <- list(red = 1, yellow = 2, blue = 3)
> values
$red
[1] 1

$yellow
[1] 2

$blue
[1] 3

There is also a vector containing the diffrent "colors" as character
strings:
> colors <- c("red", "red", "blue",
"yellow", "red", "blue")
> colors
[1] "red"    "red"    "blue"   "yellow"
"red"    "blue"

Now i can attach the list values to R:
> attach(values)
> red
[1] 1

etc...

Now to my problem: How can I make R in a simple way to evaluate the strings
"red", "blue" etc. as variables, returning their numeric
values ?
As result I want to get a vector containing the values of the colors like this
one:
> values.colors
[1] 1 1 3 2 1 3

Thanks a lot,
greetings Robin











	[[alternative HTML version deleted]]

"Robin Gruna" <robin_gruna at hotmail.com> writes:
> I have the following problem: I have a list as follows,
> 
> > values <- list(red = 1, yellow = 2, blue = 3)
> 
> > values
> $red
> [1] 1
> 
> $yellow
> [1] 2
> 
> $blue
> [1] 3
> 
> There is also a vector containing the diffrent "colors" as
character strings:
> 
> > colors <- c("red", "red", "blue",
"yellow", "red", "blue")
> > colors
> [1] "red"    "red"    "blue"  
"yellow" "red"    "blue"
> 
> Now i can attach the list values to R:
> 
> > attach(values)
> > red
> [1] 1
> 
> etc...
> 
> Now to my problem: How can I make R in a simple way to evaluate the strings
"red", "blue" etc. as variables, returning their numeric
values ?
> As result I want to get a vector containing the values of the colors like
this one:
> 
> > values.colors
> [1] 1 1 3 2 1 3
Forget about the attach() business, and do

values <- unlist(values) # or values <- c(red = 1, yellow = 2, blue = 3)
values.colors <- values[colors]

If you insist on going via variables, try

sapply(colors, get)

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