Although not loading the needless data is the optimal solution (see the Loading a subset of text files and Loading data from databases sections in Chapter 1, Hello, Data!), we often have to filter the original dataset inside R. This can be done with the traditional tools and functions from base R, such as subset
, by using which
and the [
or [[
operator (see the following code), or for example with the SQL-like approach of the sqldf
package:
> library(sqldf) > sqldf("SELECT * FROM mtcars WHERE am=1 AND vs=1") mpg cyl disp hp drat wt qsec vs am gear carb 1 22.8 4 108.0 93 3.85 2.320 18.61 1 1 4 1 2 32.4 4 78.7 66 4.08 2.200 19.47 1 1 4 1 3 30.4 4 75.7 52 4.93 1.615 18.52 1 1 4 2 4 33.9 4 71.1 65 4.22 1.835 19.90 1 1 4 1 5 27.3 4 79.0 66 4.08 1.935 18.90 1 1 4 1 6 30.4 4 95.1 113 3.77 1.513 16.90 1 1 5 2 7 21.4 4 121.0 109 4.11 2.780 18.60 1 1 4 2
I am sure that all readers who have...