Reference variables by string in for loop

Dear R Users,

I am trying to get the following to work better:

namevec <- c("one", "two", "three")
for (name in namevec) {
? ?namedf <- eval(parse(text=paste(name, "_df", sep="")))
? ?...
? ?...
}

The rationale behind it being that I created variables with names
one_df, two_df and three_df earlier in the same script which I want to
reference inside the for loop. ?Is there a more elegant way to do this?

Yes, one elegant way to do it would be using a named list instead of
separate variables.

X <- list()
X$one_df <- "something"
X[["two_df"]] <- "something else"
NAME <- "one_df"
X[[NAME]]
NAME <- "two_df"
X[[NAME]]
#etc

# the for loop could then be: for(name in names(X)) ... or for(element in X)

Another way (not elegant but better and shorter than the eval-parse
way) is to use get. ?get

Best regards,

Kenn

Hi Michael.
This is a classic :-)

ObjectsOfInterest<- list(one_df, two_df, three_df)
for(namedf in ObjectsOfInterest){...}

or probably even better
sapply(ObjectsOfInterest, function(namedf){...})

hth.


Nick Sabbe
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-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Michael Bach
Sent: vrijdag 29 april 2011 12:03
To: r-help at r-project.org
Subject: [R] Reference variables by string in for loop

Dear R Users,

I am trying to get the following to work better:

namevec <- c("one", "two", "three")
for (name in namevec) {
    namedf <- eval(parse(text=paste(name, "_df", sep="")))
    ...
    ...
}

The rationale behind it being that I created variables with names
one_df, two_df and three_df earlier in the same script which I want to
reference inside the for loop.  Is there a more elegant way to do this?

Best Regards,
Michael Bach

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"Nick Sabbe" <nick.sabbe at ugent.be> writes:

ObjectsOfInterest<- list(one_df, two_df, three_df)
for(namedf in ObjectsOfInterest){...}

I see. This is also more readable and traceable for others.

or probably even better
sapply(ObjectsOfInterest, function(namedf){...})

I like this one for its functional style.

hth.

It did, thanks.

Kind Regards,
Michael Bach

Kenn Konstabel <lebatsnok at gmail.com> writes:

Another way (not elegant but better and shorter than the eval-parse
way) is to use get. ?get

This one is handy for interactive use, thanks for the hint.

Kind Regards,
Michael Bach