On Nov 1, 2009, at 1:59 AM, Patrick Connolly wrote:
On Sun, 01-Nov-2009 at 01:20AM -0500, Jason Priem wrote:
I've got a data frame describing comments on an electronic journal,
wherein each row is a unique comment, like so:
commentID author articleID
1 1 smith 2
2 2 jones 3
3 3 andrews 2
4 4 jones 1
5 5 johnson 3
6 6 smith 2
Let's call that dataframe x
I want know the number of unique authors per article. I can get a
table
of article frequencies with table(articleID), but I can't figure
out how
to count frequencies in a different column. I'm sure there's an easy
way, but I guess I'm too new at this to find it.
I'm not clear what you require, but maybe it's this:
with(x, table(articleID, author))
articleID andrews johnson jones smith
1 0 0 1 0
2 1 0 0 2
3 0 1 1 0
Is that anything like what you're after?
You've had two guesses so far and my guess increments the count.
Were you attempting to specify this?
df1 <- read.table(textConnection("commentID author articleID
1 1 smith 2
2 2 jones 3
3 3 andrews 2
4 4 jones 1
5 5 johnson 3
6 6 smith 2"), header=T)
> lapply( lapply(tapply(df1$author, df1$articleID, I), unique) ,
length)
$`1`
[1] 1
$`2`
[1] 2
$`3`
[1] 2
Or delivered in matrix form (and using Connolly's approach as
intermediate:
> apply( with(df1, table(articleID, author)), 1, function(x) sum(x>0) )
1 2 3
1 2 2
--
~
.~
.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.
___ Patrick Connolly
--
David Winsemius, MD
Heritage Laboratories
West Hartford, CT
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