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"
> b <- mtcars[1:5, ]
> class(b)
[1] "data.frame"


Thanks a lot,
Mike

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