I have a data frame that looks as follows.

df <- data.frame(city=c("Houston", "Houston", "El Paso", "Waco", Houston",
"Plano", "Plano")

What I want to do is get a list of the city values. Currently, when I run
df$city, I get all the values.

I just want to know the four cities that appear.
So instead of:  "Houston", "Houston", "El Paso", "Waco", Houston", "Plano",
"Plano"

I want: "Houston", "El Paso", "Waco", "Plano"


I'm running R 2.13 on Ubuntu 10.10


Abraham

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