[R] reorganizing a data frame
dmurdoch at pair.com
Sat Jul 8 16:35:03 CEST 2000
On Sat, 8 Jul 2000 06:58:29 -0500, you wrote:
> Thanks for the response! I'm not sure that
> I completely understand your suggestion.
> I start with a dataframe called "oldstock"
> (three columns: date, ticker, close) and I want to
> turn this into a matrix called "newstock" with
> rows and length(unique(stockdata[,"ticker"])) columns.
> The names of the rows will be the dates, and the names of
> the columns will be the tickers, and the value of
> will either be the close price for the ticker on the date
> in question, or NA if we don't have a close price for the
> ticker on that date.
> I'm not that familiar with how tapply works so
> I don't see exactly how to apply your idea to "oldstock"
> in order to get out "newstock". What should
> the arguments of tapply be?
>> The tapply() function is what you want. I think the code would be
Change this to
I had a typo in what I wrote before: INTC should only have appeared
once. (It happened because I couldn't remember the order of the args,
and when it didn't work the first way, I moved INTC to the start, but
forgot to delete the second entry.)
The basic use of tapply for a 2 way table takes these arguments:
tapply( x, # The variable to do the calculations on.
list(rowvar, colvar), # The variables to determine the row
func) # The function that gives the table entry
This produces a table with row labels from rowvar, column labels from
colvar. The table entry at row r column c is func(x[rowvar=r &
I hope this helps.
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