Evaluating a String to Determine Variable and Assigning Value in R

Question

I want to be able to be able to create a new variable in a data.frame that is named based on an existing string. So, for example, if the new variable is Q7A what I have tried to do is the following:

question <- "Q7A"
Q <- parse( text = paste("data$", question, sep = ""))
eval(Q) <- 3

What I want this to be interpreted as is:

data$Q7A <- 3

But I get the following error message: Error in eval(Q) <- 3 : could not find function "eval<-"

Are you doing a course that has this as a problem? Suspiciously similar to the question I link to as possible duplicate. — Gavin Simpson, Jul 22 '13 at 19:17

score 3 · Accepted Answer · answered Jul 22 '13 at 18:58

3

Don't use $.

data[,question] <- 3

Always remember fortune(106):

If the answer is parse() you should usually rethink the question.
   -- Thomas Lumley
      R-help (February 2005)

answered Jul 22 '13 at 18:58

joran

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Even more eccentric: Computing what data.frame() is assigned to, e.g. using `my.df – texb Jul 22 '13 at 19:17

Evaluating a String to Determine Variable and Assigning Value in R

1 Answers1