subset arg in (modified) evalq

Hi,

When using evalq to evaluate expressions within a say data.frame context I often wish there was a 'subset' argument, much like in lm() or any ather advanced regression model. I would be grateful for a tip how to do this.

Here is an illustration of what I want:

n <- 100
data <- data.frame(x=rnorm(n), y=rnorm(y), z=rnorm(z))

# this works
evalq({ i <- 0<x; summary(y[i] + z[i]) }, data)

# I want to do the above w/o explicit subscripting, e.g.
myevalq(summary(y + z), subset=0<x, data)

Thanks,
Vadim

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