Calculate average based on condition in r : I have a table 

    Country	ClaimId	ClaimItem	ClaimAmt
    IN	    C1	    1	        100
    IN	    C1	    2	        200
    US	    C2	    1	        100
    US	    C2	    2	        100
    US	    C2	    3	        100
    US	    C3	    1	        100
    US	    C3	    2	        100
    UK	    C4	    1	        100
    UK	    C4	    2 	        200
    UK	    C1	    1	        100
    UK	    C1	    2	        200

Here I want to calculate average per claimID such that my expected table looks like


    Country	ClaimId	ClaimItem	ClaimAmt  Avg
    IN	    C1	    1	        100       300
    IN	    C1	    2	        200       300
    US	    C2	    1	        100       250
    US	    C2	    2	        100       250
    US	    C2	    3	        100       250
    US	    C3	    1	        100       250
    US	    C3	    2	        100       250
    UK	    C4	    1	        100       300
    UK	    C4	    2 	        200       300
    UK	    C1	    1	        100       300
    UK	    C1	    2	        200       300
Any idea on how the expected table can be achieved.
Thanks

Here is the sample

    > dput(claims)
    structure(list(Country = structure(c(1L, 1L, 3L, 3L, 3L, 3L, 
    3L, 2L, 2L, 2L, 2L), .Label = c("IN", "UK", "US"), class = "factor"), 
        ClaimId = structure(c(1L, 1L, 2L, 2L, 2L, 3L, 3L, 4L, 4L, 
        1L, 1L), .Label = c("C1", "C2", "C3", "C4"), class = "factor"), 
        ClaimItem = c(1L, 2L, 1L, 2L, 3L, 1L, 2L, 1L, 2L, 1L, 2L), 
        ClaimAmt = c(100L, 200L, 100L, 100L, 100L, 100L, 100L, 100L, 
        200L, 100L, 200L)), .Names = c("Country", "ClaimId", "ClaimItem", 
    "ClaimAmt"), class = "data.frame", row.names = c(NA, -11L))

