Selecting columns

To pick out single or multiple columns use the select() function.

The select() function expects a dataframe as it’s first input (‘argument’, in R language), followed by the names of the columns you want to extract with a comma between each name.

It returns a new dataframe with just those columns, in the order you specified:

head(
  select(mtcars, cyl, hp)
)
                  cyl  hp
Mazda RX4           6 110
Mazda RX4 Wag       6 110
Datsun 710          4  93
Hornet 4 Drive      6 110
Hornet Sportabout   8 175
Valiant             6 105

Saving a subset of the data

Because dplyr functions return a new dataframe, we can assign the results to a variable:

justcylandweight <- select(mtcars, cyl, wt)
summary(justcylandweight)
      cyl              wt       
 Min.   :4.000   Min.   :1.513  
 1st Qu.:4.000   1st Qu.:2.581  
 Median :6.000   Median :3.325  
 Mean   :6.188   Mean   :3.217  
 3rd Qu.:8.000   3rd Qu.:3.610  
 Max.   :8.000   Max.   :5.424

Excluding columns

If you want to keep most of the columns — perhaps you just want to get rid of one and keep the rest — put a minus (-) sign in front of the name of the column to drop. This then selects everything except the column you named:

# Note we are just dropping the Ozone column
head(select(airquality, -Ozone))
  Solar.R Wind Temp Month Day
1     190  7.4   67     5   1
2     118  8.0   72     5   2
3     149 12.6   74     5   3
4     313 11.5   62     5   4
5      NA 14.3   56     5   5
6      NA 14.9   66     5   6

Matching specific columns

You can use a patterns to match a subset of the columns you want. For example, here we select all the columns where the name contains the letter d:

head(select(mtcars, contains("d")))
                  disp drat
Mazda RX4          160 3.90
Mazda RX4 Wag      160 3.90
Datsun 710         108 3.85
Hornet 4 Drive     258 3.08
Hornet Sportabout  360 3.15
Valiant            225 2.76

And you can combine these techniques to make more complex selections:

head(select(mtcars, contains("d"), -drat))
                  disp
Mazda RX4          160
Mazda RX4 Wag      160
Datsun 710         108
Hornet 4 Drive     258
Hornet Sportabout  360
Valiant            225

Other methods of selection

As a quick reference, you can use the following ‘verbs’ to select columns in different ways:

  • starts_with()
  • ends_with()
  • contains()
  • everything()

See the help files for more information (type ??dplyr::select into the console).