r - data.table object trying to effect ddply like operation using by() -

i've searched quite bit no avail, let alone trying make work myself, without further do:

i have data.table:

 dt = data.table(date=rep(c(as.date("2010-01-01"),as.date("2010-01-02")), each=3),       bucket=rep(c("bucket1","bucket2","bucket3"),each=2), kbucket=c("(0,.5]","(.5,1]","(1,1.5]","(1.5,2]","(1.5,2]","(2.5,3]"),vol=1:6,o=10:15,m=20:25) 

which looks like:

         date  bucket kbucket vol  o  m 1: 2010-01-01 bucket1  (0,.5]   1 10 20 2: 2010-01-01 bucket1  (.5,1]   2 11 21 3: 2010-01-01 bucket2 (1,1.5]   3 12 22 4: 2010-01-02 bucket2 (1.5,2]   4 13 23 5: 2010-01-02 bucket3 (1.5,2]   5 14 24 6: 2010-01-02 bucket3 (2.5,3]   6 15 25 

i've used ddply so, on df, facsimile of dt, data frame:

out <- ddply(df,.(date,bucket,kbucket),wrap_summarize) 

where wrap_summarize defined as:

 wrap_summarize = function(x)                     {                         out <-  summarize(  x,                        n = length(x$date),                        sumvol = sum(x$vol),                        sumo = sum(x$o),                        avgm = mean(x$m,na.rm=true))                    } 

to get

        date  bucket kbucket n sumvol sumo avgm 1 2010-01-01 bucket1  (.5,1] 1      2   11   21 2 2010-01-01 bucket1  (0,.5] 1      1   10   20 3 2010-01-01 bucket2 (1,1.5] 1      3   12   22 4 2010-01-02 bucket2 (1.5,2] 1      4   13   23 5 2010-01-02 bucket3 (1.5,2] 1      5   14   24 6 2010-01-02 bucket3 (2.5,3] 1      6   15   25 

this desired result.

the actual data has structure hundreds of thousands of rows. need data.table methods. try this:

test <- dt[,list(n=length(dt$date),sumvol=sum(dt$vol),sumo=sum(dt$o),avgm=mean(dt$m,na.rm=t)), by=list(date,bucket,kbucket)] 

only get, not desired:

         date  bucket kbucket n sumvol sumo avgm 1: 2010-01-01 bucket1  (0,.5] 6     21   75 22.5 2: 2010-01-01 bucket1  (.5,1] 6     21   75 22.5 3: 2010-01-01 bucket2 (1,1.5] 6     21   75 22.5 4: 2010-01-02 bucket2 (1.5,2] 6     21   75 22.5 5: 2010-01-02 bucket3 (1.5,2] 6     21   75 22.5 6: 2010-01-02 bucket3 (2.5,3] 6     21   75 22.5 

i think need use .sd here, @ point, thought best ask , share problem if not efficient solution. in advance!

you're looking this:

dt[,list(     .n,     sumvol=sum(vol),     sumo=sum(o),     avgm=mean(m,na.rm=t) ),by=list(date,bucket,kbucket)] 

which gives

#          date  bucket kbucket n sumvol sumo avgm # 1: 2010-01-01 bucket1  (0,.5] 1      1   10   20 # 2: 2010-01-01 bucket1  (.5,1] 1      2   11   21 # 3: 2010-01-01 bucket2 (1,1.5] 1      3   12   22 # 4: 2010-01-02 bucket2 (1.5,2] 1      4   13   23 # 5: 2010-01-02 bucket3 (1.5,2] 1      5   14   24 # 6: 2010-01-02 bucket3 (2.5,3] 1      6   15   25