[R] How to parse a string into the symbol for a data frame object

Darren Weber darren.weber.lists at gmail.com
Sun Aug 19 22:37:45 CEST 2007

 I have several data frames, eg:

> df1 <- data.frame(x=seq(0,10), y=seq(10,20))
> df2 <- data.frame(a=seq(0,10), b=seq(10,20))

It is common to create loops in R like this:

> for(df in list(df1, df2)){ #etc. }

This works fine when you know the name of the objects to put into the
list.  I assume that the order of the objects in the list is respected
through the loop.  Inside the loop, the objects of the list are
'dereferenced' using 'df' but, to my knowledge, there is no way to
tell whether 'df' is a current representation of 'df1' or 'df2'
without some additional book keeping.

In addition, I really want to use 'paste' within the loop to create a
new string value that will have the symbol name of a data frame to be
"dereferenced," e.g.:

> for(n in c(1, 2)){ dfString <- paste('df', n, sep=""); print(eval(dfString)) }

[1] "df1"
[1] "df2"

This is not what I want.  I have read through the documentation on
eval and similar commands like substitute and quote.  I program
regularly, but I do not understand these constructs in R.  I do not
understand the R framework for parsing and evaluation and I don't have
a lot of time right now to get lost in this detail.  I could really
use some help to get the string values in my loop to be parsed into
symbols that refer to the data frame objects df1 and df2.  How is this

Best, Darren

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