[R] ddply question

[Felipe Carrillo]

I apologize about cross posting but my question keeps bouncing back from the list
 
 How come pct doesn't work in this ddply call?
I am trying to get a percent of 'TotalCount' by SampleDate and Age
 library(plyr)
b <- structure(list(SampleDate = structure(c(1L, 1L, 1L, 1L, 1L, 1L,
1L, 1L, 1L), .Label = "5/8/1996", class = "factor"), TotalCount = c(1L,
2L, 1L, 1L, 4L, 3L, 1L, 10L, 3L), ForkLength = c(61L, 22L, NA,
NA, 72L, 34L, 100L, 23L, 25L), TotalSalvage = c(12L, 24L, 12L,
12L, 17L, 23L, 31L, 12L, 15L), Age = c(1L, 0L, NA, NA, 1L, 0L,
1L, 0L, 0L)), .Names = c("SampleDate", "TotalCount", "ForkLength",
"TotalSalvage", "Age"), class = "data.frame", row.names = c(NA,
-9L))
b
ddply(b,.(SampleDate,Age),summarise,salvage=sum(TotalSalvage),pct=TotalCount/sum(TotalCount))
Error: expecting result of length one, got : 4
 
#Computing TotalCount inside ddply works but the pct seems wrong...
ddply(b,.(SampleDate,Age),summarise,salvage=sum(TotalSalvage),Count=sum(TotalCount),pct=Count/sum(Count))
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