On 12-04-2013, at 21:32, C W <tmrs...@gmail.com> wrote: > Dear list, > > I want the 1st, 2nd, 5th, and 6th columns of mtcars. After copying them, > the columns become numeric class rather than data frame. > > But, when I copy rows, they data frame retains its class. Why is this? I > don't see why copying rows vs columns is so different. > >> class(mtcars) > [1] "data.frame" >> head(mtcars) > mpg cyl disp hp drat wt qsec vs am gear carb > Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4 > Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4 > Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1 > Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1 > Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2 > Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1 >> a <- mtcars$mpg >> class(a) > [1] "numeric"
Here you are assigning a single column of mtcars, which is a numeric vector, to another object. So that is a numeric vector. >> b <- mtcars[1:5, ] >> class(b) > [1] "data.frame" > Here you are assigning a couple of rows of the complete dataframe and the result is a dataframe. If you want the 1st, 2nd, 5th, and 6th columns of mtcars in a new datafrmae why don't you do this: a <- mtcars[,c(1,2,5,6)] then > class(a) [1] "data.frame" Berend ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
