R data frame: add values in common rows

Question

I have a data frame like this .

> df1
  portfolio       date ticker quantity price
1      port 2010-01-01   AAPL      100    10
2      port 2010-01-01   AAPL      200    10
3      port 2010-01-01   AAPL      400    11

If the rows of df1 except quantity are same, then add the quantity of common rows. I mean, i need the following output

portfolio       date ticker quantity price
1      port 2010-01-01   AAPL      300    10
3      port 2010-01-01   AAPL      400    11

How can i do that? Thanks..

Answer 1

Here you go... :-)

For plyr :

ddply(df, .(portfolio, date, ticker, price),summarize, quantity=sum(quantity))

For data.table :

dt <- data.table(df)
dt[,list(quantity=sum(quantity)),by=list(portfolio,date,ticker,price)]

There may be a more concise way to express the list of grouping variables. Otherwise, the aggregate solution is much more elegant.

Answer 2

Use aggregate. Assuming your data.frame is called "mydf":

> aggregate(quantity ~ ., mydf, sum)
  portfolio       date ticker price quantity
1      port 2010-01-01   AAPL    10      300
2      port 2010-01-01   AAPL    11      400

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Of course, we should all now wait for the data.table and ddply versions to populate the answers list....