R: passing values to eval in nested functions

Question

I want to pass some query to lower level function that uses 'eval'. Here's a simplified example:

f1 <- function(x, q) eval(substitute(q), envir=x)
f2 <- function(x, q) f1(x, q)

What's happening:

> x <- data.frame(a=1:5)
> f1(x, a<3)
[1]  TRUE  TRUE FALSE FALSE FALSE
> f2(x, a<3)
Error in eval(expr, envir, enclos) : object 'a' not found

While I would like f2 to produce the same output like f1. Argument 'q' is some general query that is going to be evaluated on 'x'. I keep the example simple and general but I want to extend it's behavior on more complicated functions and queries. The thing that matters to me is how to "pass" the query "q" so that eval knows what to do with it no matter how many levels of nested functions there were before.

How can I do that? Thanks!

Is the body of f2 the only thing you are willing to modify? — flodel
– flodel, Commented Oct 10, 2014 at 10:57
Sorry I'm not sure what you mean...? I can modify any of f1 or f2 functions, the only thing that matters is they both work the same with the same arguments where 'q' is some general query I want to evaluate on 'x'. — Tim
– Tim, Commented Oct 10, 2014 at 11:04

flodel · Accepted Answer · 2014-10-10 11:06:08Z

2

You can do:

f1 <- function(x, q) eval(substitute(q), envir=x)
f2 <- function(x, q) eval(substitute(f1(x, q)))

y <- data.frame(a=1:5)
f1(y, a<3)
f2(y, a<3)

answered Oct 10, 2014 at 11:06

flodel

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Comments

JARO · Accepted Answer · 2014-10-10 10:42:08Z

0

Because you defined just x. You need:

> f2(x, x$a<3)
> [1]  TRUE  TRUE FALSE FALSE FALSE

answered Oct 10, 2014 at 10:42

JARO

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1 Comment

Tim Over a year ago

It is a simplified example. In general I would like the functions to do much more complicated stuff, so I want to pass the query 'q' as-is to the lower level function and evaluate it, so it does work the same in f1 and f2 with using the same arguments.

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