[R] 3 classification variables and one string variable

[Taka Matzmoto]

Dear R users
I have 3 classification variables (string type) and one string variable in a 
data.frame (x).

the first factor is a region (north, south, west, and east) (4 levels)
the second factor is a market type (A, B, C, and D) (4 levels)
the third factor is a item type (w, x, y, z) (4 levels)
the string variable is a seller first name.

My goal is to create a string vector consisting of seller first names for 
each cell of  4*4*4 contingency table. Some of the cells are empty.

For example, w type ITEM in B market in North region = c("John", "Smith")
I would like to create a name for the string vector using the three factor 
names (e.g., north.B.w)
I tried to use table(). It didn't work well. I could use some long tedious 
method like below but it doesn't look good.

north.B.w.ind <- x$region == "Noth" & x$market == "B" & x$item == "w"
north.B.w <- x[north.B.w.ind, "name"]


Any help will be appreciated.

Thanks

Taka,

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