This has come up a number of times in my conversations with users, and
I don't believe that there is a good GUI solution for such a general
concept (Though feel free to prove me wrong). You are going to have to
type things out.
We can do general variable computations with R in the console. Lets
start with some data:
data(mtcars)
Now, we can create a new variable "newvar" in mtcars which is the sum
of "mpg" and "cyl" with
mtcars$newvar <- mtcars$mpg + mtcars$cyl
note the dollar signs. They mean that you are looking in the
data.frame on the left hand side for the variable on the right hand
side. You can get a little notational simplification for statements
with many variable using within:
mtcars <- within(mtcars, newvar2 <- mpg + cyl)
Conditional computations can be done using ifelse
mtcars$condvar <- ifelse( mtcars$cyl==8 & mtcars$mpg < 18, "gas
guzzler", "Non gas guzzler")
this says that if a car is 8 cylenders and has under 18 mpg, then it
is a "gas guzzler".
all told, your mtcars should now look like:
mpg cyl disp hp drat wt qsec vs am gear
carb newvar newvar2 condvar
Mazda RX4 21.0 6 160.0 110 3.90 2.620 16.46 0 1 4
4 27.0 27.0 Non gas guzzler
Mazda RX4 Wag 21.0 6 160.0 110 3.90 2.875 17.02 0 1 4
4 27.0 27.0 Non gas guzzler
Datsun 710 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4
1 26.8 26.8 Non gas guzzler
Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3
1 27.4 27.4 Non gas guzzler
Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3
2 26.7 26.7 Non gas guzzler
Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3
1 24.1 24.1 Non gas guzzler
Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3
4 22.3 22.3 gas guzzler
Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4
2 28.4 28.4 Non gas guzzler
Merc 230 22.8 4 140.8 95 3.92 3.150 22.90 1 0 4
2 26.8 26.8 Non gas guzzler
Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4
4 25.2 25.2 Non gas guzzler
Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4
4 23.8 23.8 Non gas guzzler
Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3
3 24.4 24.4 gas guzzler
Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3
3 25.3 25.3 gas guzzler
Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3
3 23.2 23.2 gas guzzler
Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3
4 18.4 18.4 gas guzzler
Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3
4 18.4 18.4 gas guzzler
Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3
4 22.7 22.7 gas guzzler
Fiat 128 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4
1 36.4 36.4 Non gas guzzler
Honda Civic 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4
2 34.4 34.4 Non gas guzzler
Toyota Corolla 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4
1 37.9 37.9 Non gas guzzler
Toyota Corona 21.5 4 120.1 97 3.70 2.465 20.01 1 0 3
1 25.5 25.5 Non gas guzzler
Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3
2 23.5 23.5 gas guzzler
AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3
2 23.2 23.2 gas guzzler
Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3
4 21.3 21.3 gas guzzler
Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3
2 27.2 27.2 Non gas guzzler
Fiat X1-9 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4
1 31.3 31.3 Non gas guzzler
Porsche 914-2 26.0 4 120.3 91 4.43 2.140 16.70 0 1 5
2 30.0 30.0 Non gas guzzler
Lotus Europa 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5
2 34.4 34.4 Non gas guzzler
Ford Pantera L 15.8 8 351.0 264 4.22 3.170 14.50 0 1 5
4 23.8 23.8 gas guzzler
Ferrari Dino 19.7 6 145.0 175 3.62 2.770 15.50 0 1 5
6 25.7 25.7 Non gas guzzler
Maserati Bora 15.0 8 301.0 335 3.54 3.570 14.60 0 1 5
8 23.0 23.0 gas guzzler
Volvo 142E 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4
2 25.4 25.4 Non gas guzzler