R help - Jan 2011 - Extracting user specified variables from data frame to use as function arguments

Hello All;

I am writing an R program in the form of a function to find out the summary
statistics for response variable(s) in a data frame.

I need to accept variable names from the data as arguments and use them
inside the function for various tasks. The dataset name is also one of the
arguments to the program. The tasks include merging two datasets,
transposing a dataset or finding the summary stats of response variable(s)
using the input variables as the 'by' variables.

The variables specified as argument for the function are taken to be
character strings and I have not been able to use these to extract the
corresponding variables.

As an example, suppose I have an argument 'merge_by' which is used to
specify the variables used to merge two datasets. Typically, the input is
"an period" (with the double quotes) but could be more or less
variables
than that.

How do I input the user specified variables and use them for tasks like
merging, transposing etc.?

A similar problem is with specifying the user defined by variables in
summaryBy.

I have played around with substitute, parse, eval etc. but without success.

Any suggestions?

Thanks

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