ddply to count frequency of combinations
On Jun 21, 2011, at 2:30 PM, Idris Raja wrote:
I have a dataframe df with two columns x and y. I want to count the
number
of times a unique x, y combination occurs.
For example
x<- c(1,2,3,4,5,1,2,3,4)
y<- c(1,2,3,4,5,1,2,4,1)
df<-as.data.frame(cbind(x, y))
#what is the correct way to use ddply for this example?
ddply(df, c('x','y', summarize, ??)
#desired output -- format and order doesn't matter
# (x, y) count
#--------------------
# (1, 1) 2
# (2, 2) 2
# (3, 3) 1
# (4, 4) 1
# (5, 5) 1
# (2, 3) 1
# (3, 4) 1
# (4, 1) 1
Here's a non plyr approach:
> tab.df <- as.data.frame(table(df))
> tab.df[tab.df$Freq > 0, ]
x y Freq
1 1 1 2
4 4 1 1
7 2 2 2
13 3 3 1
18 3 4 1
19 4 4 1
25 5 5 1
Did you know that there is a newsgroup specifically set up for plyr
questions?
manipulatr at googlegroups.com
David Winsemius, MD West Hartford, CT