R-Help(Aggregate function): Multiple functions for different collumns

I'm trying to reduce the resolution or remove duplicate time stamps for the
same symbols in the following sample file, in a way such that the new price
is a volume weighted average for that second(timestamp) and the new volume
is the sum of all volumes within that second.

I'm trying to use sapply and aggregate separately but having trouble with
the function. I want that the function should do a volume weighted avg for
the price column in the subgroup(where timestamps and symbols are same) but
a sum of volume in that group. How do I achieve both goals simultaneously.

I did a lot of research on the mailing archives and spent hours on reading
the help/faq but couldn't figure it out.

Here's my codes that is working:-

tmp1.split <- sapply(split(tmp1, tmp1$symbol),
function(x){weighted.mean(tmp1$price, tmp1$volume)})
tmp1.ag <- aggregate(tmp1, by=list(tmp1$symbol, tmp1$time),
function(x){weighted.mean(tmp5$price, tmp5$volume)})

How do I go ahead now(I'm confused and new to R)
How do I write functions that handle multiple columns differently.

tmp1 #my dataframe

? sno ? ? symbol series ? ? time ? price volume
1 ? ?1 BHARTIARTL ? ? EQ 18:15:05 ?600.00 ? ? ?1
2 ? ?2 BHARTIARTL ? ? EQ 18:15:05 ?600.00 ? ? 99
3 ? ?3 ? GLENMARK ? ? EQ 18:15:05 ?238.10 ? ? ?5
4 ? ?4 ? HINDALCO ? ? EQ 18:15:05 ? 43.75 ? ?100
5 ? ?5 BHARTIARTL ? ? EQ 18:15:05 ?600.00 ? ? ?1
6 ? ?6 ? ? ? BHEL ? ? EQ 18:15:05 1100.00 ? ? 11
7 ? ?7 ? HINDALCO ? ? EQ 18:15:06 ? 43.20 ? ? ?1
8 ? ?8 CHAMBLFERT ? ? EQ 18:15:06 ? 46.00 ? ? 10
9 ? ?9 CHAMBLFERT ? ? EQ 18:15:06 ? 46.00 ? ? 90
10 ?10 BAJAUTOFIN ? ? EQ 18:15:06 ? 80.00 ? ?100

Thanks

--
Jatin Patni
Tel: 91 9833 2180 52
jatinpatni at gmail.com
www.jatinpatni.co.nr

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