On Fri, 2 Sep 2016, Bert Gunter wrote:
[snip]
The "trick" is to use tapply() to select the necessary row indices of
your data frame and forget about all the do.call and rbind stuff. e.g.
I agree the way to go is "select the necessary row indices" but I get
there a different way. See below.
set.seed(1001)
df <- data.frame(f =factor(sample(LETTERS[1:4],100,rep=TRUE)),
+ g <- factor(sample(letters[1:6],100,rep=TRUE)),
+ y = runif(100))
ix <- seq_len(nrow(df))
ix <- with(df,tapply(ix,list(f,g),function(x)x[length(x)]))
ix
a b c d e f
A 94 69 100 59 80 87
B 89 57 65 90 75 88
C 85 92 86 95 97 62
D 47 73 72 74 99 96
jx <- which( !duplicated( df[,c("f","g")], fromLast=TRUE ))
xtabs(jx~f+g,df[jx,]) ## Show equivalence to Bert's `ix'
g
f a b c d e f
A 94 69 100 59 80 87
B 89 57 65 90 75 88
C 85 92 86 95 97 62
D 47 73 72 74 99 96
Chuck
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