[R] data frame manipulation ddply

[arnaud Gaboury]

Dear group,

Here is my data frame:


futures <-
structure(list(DESCRIPTION = c("CORN Jul/10", "CORN Jul/10", 
"CORN Jul/10", "CORN Jul/10", "CORN Jul/10", "LIVE CATTLE Aug/10", 
"LIVE CATTLE Aug/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10", 
"SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10", "SUGAR NO.11 Jul/10"
), CREATED.DATE = structure(c(18403, 18406, 18406, 18406, 18406, 
18407, 18408, 18406, 18407, 18407, 18407, 18407), class = "Date"), 
    QUANTITY = c(1, 1, 1, 1, 1, 3, 1, 1, 1, 1, 1, 1), SETTLEMENT =
c("373.2500", 
    "373.2500", "373.2500", "373.2500", "373.2500", "90.7750", 
    "90.7750", "14.9200", "14.9200", "14.9200", "14.9200", "14.9200"
    )), .Names = c("DESCRIPTION", "CREATED.DATE", "QUANTITY", 
"SETTLEMENT"), row.names = c(NA, 12L), class = "data.frame")

Here is the line I pass :

>PosFut=ddply(futures, c("DESCRIPTION","SETTLEMENT"), summarise, POSITION=
sum(QUANTITY))[,c(1,3,2)]

And here the result :

PosFut <-
structure(list(DESCRIPTION = structure(1:3, .Label = c("CORN Jul/10", 
"LIVE CATTLE Aug/10", "SUGAR NO.11 Jul/10"), class = "factor"), 
    POSITION = c(5, 4, 5), SETTLEMENT = structure(c(2L, 3L, 1L
    ), .Label = c("14.9200", "373.2500", "90.7750"), class = "factor")),
.Names = c("DESCRIPTION", 
"POSITION", "SETTLEMENT"), class = "data.frame", row.names = c(NA, 
-3L))

I can no more use ddply, as this above command line is in a function, and
this line should be able to work with a data frame with zero rows, and in
this case ddply doesn't work.
Any suggestion how to obtain the same result without ddply?

TY for any help.