Consider
items<-alist(2^1,2^2,2^3,2^3)
Suppose that I want to construct a data frame where the unevaluated expressions in items are one column and their evaluated versions are in another. In other words, I want something like:
items results
2^1 1
2^2 4
2^3 8
2^3 8
as my outputs. I would use the row.names argument, but it rejects duplicated names and cannot be convinced otherwise.
The natural thing to try is
items<-alist(2^1,2^2,2^3,2^3)
outs<-sapply(items,eval)
data.frame(items=items,results=outs)
but the outputs appears to treat each element of the alist as if it were a column name:
> data.frame(items=items,results=outs)
items.2.1 items.2.2 items.2.3 items.2.3.1 results
1 2 4 8 8 2
2 2 4 8 8 4
3 2 4 8 8 8
4 2 4 8 8 8
lapply does not fair any better:
> outs<-lapply(items,eval)
> data.frame(items=items,results=outs)
items.2.1 items.2.2 items.2.3 items.2.3.1 results.2 results.4 results.8 results.8.1
1 2 4 8 8 2 4 8 8
I am aware that I could use a matrix instead of a data frame, but that is not what I'm asking about.
@nicola's suggestion in the comment almost works, but doesn't display properly:
> data.frame(items=I(items),results=vapply(items,eval,1))
items results
1 ^, 2, 1 2
2 ^, 2, 2 4
3 ^, 2, 3 8
4 ^, 2, 3 8
If you don't care about the display, I'd use that. If you want it to display nicely, you need to convert the language objects to expression objects, e.g.
eitems <- lapply(items, as.expression)
> data.frame(items=I(eitems),results=vapply(items,eval,1))
items results
1 2^1 2
2 2^2 4
3 2^3 8
4 2^3 8
or just deparse them to character values if you don't want to be able to evaluate them again:
ditems <- sapply(items, deparse)
> data.frame(items = ditems, results=vapply(items,eval,1))
items results
1 2^1 2
2 2^2 4
3 2^3 8
4 2^3 8