[R] Conditional selection of rows
F Z
gerifalte28 at hotmail.com
Tue Nov 9 19:48:39 CET 2004
Many thanks to Gabor Grothendieck, Thomas Lumley and James Holtman for their
useful answers on this thread. The three solutions worked for the problem.
Here is a sumary of their responses (modified for consistency on notations):
>F Z <gerifalte28 <at> hotmail.com> writes:
>: Hi,
>:
>: I have a data.frame with several variables and 50,000 observations.
>: i.e.
>: data[1:2,1:7]
>: Iteration Day Production.Type tsUSusc tsASusc tsULat tsALat
>: 1 0 Generic 17965 8833053 0 0
>: 1 1 Generic 17965 8833053 0 0
>: .
>: .
>: .
>: 1 199 Generic 17237 8141028 26 23131
>: 2 127 Generic 15828 7307583 92 63463
>:
>: I would like to extract only the observations (rows) for the last "day"
>for
>: each "iteration" and store them in a data frame.
Gabor Grothendieck's solution:
subset<-do.call("rbind", by(data, data$Iteration, tail, 1))
James Holtman's solution:
subset<- by(data, data$Iteration, function(x)x[nrow(x),])
subset<-do.call('rbind',subset)
Thomas Lumley's solution:
data <- data[order(data$Iteration, data$Day, decreasing=TRUE),]
subset <- data[!duplicated(data$Iteration),]
If you are sure that the data are in order to begin with you could just
reverse the entire data set ( data <- data[nrow(data):1,] ), but I'm always
reluctant to assume this.
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