Hi folks, I am running into a problem when calling subset() on a large data.frame. One of the columns contains strings which are used as factors. R seems to automatically factor the column when the data.frame is contstructed, and this appears to not get updated when I create a subset of the table.
A minimal testcase to demonstrate the problem follows:
sample <- data.frame(c("A", "A", "A", "A", "B", "B", "B", "C", "C", "C"),
c(5,3,5,3,6,7,8,3,2,6))
names(sample) <- c("ID", "Value")
print(sample)
sample.filtered <- subset(sample, ID != "B", select=c(ID, Value))
# Or sample.filtered <- subset(sample, ID != "B", select=c(ID, Value), drop=T)
print(sample.filtered)
plot(sample.filtered)
plot(sample.filtered$Value ~ sample.filtered$ID)
print(levels(sample.filtered$ID))
print(levels(factor(sample.filtered$ID)))
plot(sample.filtered$Value ~ factor(sample.filtered$ID))
Am I doing something wrong here, or is this an R bug? How can I get
the new data.frame to update the factors, so I don't get redundant
"empty" factors on the plot by eliminating the "phantom" factors? (I
also need to remove the unused factors for other analyses, and
factoring them "by hand" seems a little redundant.)
Kind regards,
Roger
--
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