[R] How do I run the by function on an object of class "by"???

[chipmaney]

I wrote a function with some loops and avoided a third loop by using the "by"
function.  The output object is an array (or list) of class "by" that looks
like this:

>StationCover.df

Empirical.df$Quadrat: VFFF9-21
       Station Shrub Tree Woody Invasive Herb Litter Bare
  [1,]     0.0     1    1     1        0    0      0    0

Empirical.df$Quadrat: VFFF9-22
       Station Shrub Tree Woody Invasive Herb Litter Bare
  [1,]     0.0     1    1     1        0    0      0    0

Empirical.df$Quadrat: VFFF9-23
       Station Shrub Tree Woody Invasive Herb Litter Bare
  [1,]     0.0     1    1     1        0    0      0    0

etc etc.....

basically, i want to use this output object, StationCover.df as a data
object for another by() function.

However, I get the following error:
> by(StationCover.df,Quadrats.df,TotalCover)

Error in as.data.frame.default(data) :   cannot coerce class "by" into a
data.frame 

So, obviously I need to extract data.frames from my original by() function
output, StationCover.df for use in other functions.

Any suggestions on the quickest way to do this? 
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