[R] Joining Dataframes

[Matt Goff]

I am attempting to join several dataframes that summarize sampling effort  
for different samples into one large data.frame/table.
I have looked at the merge command, but have not been clever enough to  
figure out how to get it to do what I want.

A simplified example of what I am trying to do:

The dataframes I have look like this (they were generated using the table  
command)

species1.effort
            site1   site2   site3
date1     5        5       5
date2     4        5       5
date3     4        5       5

species2.effort
            site1   site2   site3
date1     7        8        6
date3     8        7        8
date4     8        8        8

I would like to join these into a table that looks something like this:

Effort
             sp1.site1  sp1.site2  sp1.site3  sp2.site1  sp2.site2   
sp2.site2
date1         5               5          5             7              
8            6
date2         4               5          5            NA           
NA         NA
date3         4               5           5           8              
7             8
date4         NA           NA        NA         8            8              
8


I have many more dates and species, but I assume whatever method works for  
this small example, would work for larger cases.

Thanks,
Matt Goff