[R] matching each row

[tathta]

I have two dataframes, the first column of each dataframe is a unique id
number (the rest of the columns are data variables).  
I would like to figure out how many times each id number appears in each
dataframe.  

So far I can use: 
length( match (dataframeA$unique.id[1], dataframeB$unique.id) )

but this only works on each row of dataframe A one-at-a-time.  

I would like to do this for all of the rows in dataframe A, and then put the
results in a new variable: dataframeA$count


I'm new to R, so please be patient with me!


Sorry if this question has already been answered, my search of the archives
only brought up one relevant post, and I didn't understand the answer to
it....  http://www.nabble.com/match-to20799206.html#a20799206


thx
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