Hi Jean - Thank you for your help. The code worked great. 

----- Original Message -----

From: "Jean V Adams [via R]" <ml-node+s789695n4647444h13@n4.nabble.com> 
To: "Sally_roman" <sroman@umassd.edu> 
Sent: Thursday, October 25, 2012 2:48:45 PM 
Subject: Re: trying ti use a function in aggregate 

Sally, 

It's great that you provided data and code. To make it even more 
user-friendly for R-help readers, supply your data as Rcode, using (for 
example) the dput() function. 

The reason you were getting all 1s with your code, is that you had told it 
to aggregate by trip, LENGTH, and species. But the data are already 
summarized by trip, LENGTH, and species, so your myfun() function is 
calculating the count/count=1 for each row. You could get rid of LENGTH 
to use your myfun() function, but the results aren't pretty ... 

with(data, aggregate(data.frame(Total=Count), data.frame(Trip_id, 
CommonName), myfun)) 

Instead, I suggest you can use the aggregate function to calculate the 
total counts, then merge these totals with your original data to calculate 
the proportions. 

# small subset of data 
data <- structure(list(Trip_id = c(230L, 230L, 230L, 230L, 230L, 230L, 
230L, 230L, 230L, 230L, 230L, 230L, 230L, 230L, 230L, 230L, 230L, 
230L, 230L, 230L, 230L, 230L, 230L, 230L, 230L, 231L, 231L, 231L, 
231L, 231L), Vessel = c("Sunlight", "Sunlight", "Sunlight", "Sunlight", 
"Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", 
"Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", 
"Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", "Sunlight", 
"Sunlight", "Sunlight", "Sunlight", "Western Venture", "Western Venture", 
"Western Venture", "Western Venture", "Western Venture"), CommonName = 
c("Shad,American", 
"Shad,American", "Shad,American", "Shad,American", "Shad,American", 
"Shad,American", "Shad,American", "Shad,American", "Shad,American", 
"Shad,American", "Herring,Blueback", "Herring,Blueback", 
"Herring,Blueback", 
"Herring,Blueback", "Alewife", "Alewife", "Alewife", "Alewife", 
"Alewife", "Alewife", "Alewife", "Alewife", "Alewife", "Alewife", 
"Alewife", "Shad,American", "Shad,American", "Shad,American", 
"Shad,American", "Shad,American"), Length = c(19L, 20L, 21L, 
23L, 26L, 27L, 30L, 33L, 34L, 37L, 20L, 21L, 22L, 26L, 17L, 18L, 
20L, 21L, 22L, 23L, 24L, 25L, 26L, 27L, 28L, 23L, 24L, 25L, 28L, 
29L), Count = c(1L, 1L, 1L, 1L, 1L, 1L, 2L, 1L, 1L, 1L, 1L, 2L, 
5L, 1L, 1L, 1L, 2L, 4L, 16L, 22L, 16L, 4L, 1L, 2L, 2L, 1L, 1L, 
1L, 2L, 2L)), .Names = c("Trip_id", "Vessel", "CommonName", "Length", 
"Count"), row.names = c(NA, -30L), class = "data.frame") 

# calculate the total count for each trip and Species 
agg <- with(data, aggregate(data.frame(Total=Count), data.frame(Trip_id, 
CommonName), sum)) 

# combine the totals with the full data frame 
data2 <- merge(data, agg) 

# then calculate proportions 
data2$Prop <- data2$Count/data2$Total 

data2 


Jean 



Sally_roman < [hidden email] > wrote on 10/25/2012 09:19:57 AM: 
> 
> Hi -I am using R v 2.13.0. I am trying to use the aggregate function to 
> calculate the percent at length for each Trip_id and CommonName. Here 
is a 

> small subset of the data. 
> Trip_id Vessel CommonName Length Count 
> 1 230 Sunlight Shad,American 19 1 
> 2 230 Sunlight Shad,American 20 1 
> 3 230 Sunlight Shad,American 21 1 
> 4 230 Sunlight Shad,American 23 1 
> 5 230 Sunlight Shad,American 26 1 
> 6 230 Sunlight Shad,American 27 1 
> 7 230 Sunlight Shad,American 30 2 
> 8 230 Sunlight Shad,American 33 1 
> 9 230 Sunlight Shad,American 34 1 
> 10 230 Sunlight Shad,American 37 1 
> 11 230 Sunlight Herring,Blueback 20 1 
> 12 230 Sunlight Herring,Blueback 21 2 
> 13 230 Sunlight Herring,Blueback 22 5 
> 14 230 Sunlight Herring,Blueback 26 1 
> 15 230 Sunlight Alewife 17 1 
> 16 230 Sunlight Alewife 18 1 
> 17 230 Sunlight Alewife 20 2 
> 18 230 Sunlight Alewife 21 4 
> 19 230 Sunlight Alewife 22 16 
> 20 230 Sunlight Alewife 23 22 
> 21 230 Sunlight Alewife 24 16 
> 22 230 Sunlight Alewife 25 4 
> 23 230 Sunlight Alewife 26 1 
> 24 230 Sunlight Alewife 27 2 
> 25 230 Sunlight Alewife 28 2 
> 26 231 Western Venture Shad,American 23 1 
> 27 231 Western Venture Shad,American 24 1 
> 28 231 Western Venture Shad,American 25 1 
> 29 231 Western Venture Shad,American 28 2 
> 30 231 Western Venture Shad,American 29 2 
> 
> My code is: 
> myfun<-function (x) x/sum(x) 
> b<-with(data,aggregate(x=list(Percent=Count),by=list 
> (Trip_id=Trip_id,Length=Length,Species=CommonName), 
> FUN="myfun")) 
> 
> My issue is that the percent is not be calculated by Trip_id and CommonName. 
> The result is that each row has a percent of 1 indicating that myfun is 
not 
> dividing by the sum of counts with a Trip_id/CommonName group. Any help 
> would be appreciated. 
> Thank you 

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