Storing filters for dplyr `filter()` in a variable

Question

I want to filter multiple dataframes on the same set of conditions. So I'd like to set those filters as a variable outside the filter() call.

For example

mtcars %>%
  filter(cyl > 4, disp > 100)

I tried doing:

filters <- c(cyl > 4, disp > 100)
mtcars %>%
  filter(filters)

But this doesn't work, because when I set the filters variable, it looks for the dataframe column.

> filters <- c(cyl > 4, disp > 100)
Error: object 'cyl' not found

What is the best way to achieve this?

Answer 1

The rlang package allows you to create unevaluated expressions that can then be swapped in using special !! notation. If you're using dplyr, you already have the key parts of rlang loaded. Note that for filter, it is good practice to be explicit about combining multiple conditions, rather than relying on filter's implicit "anding" of multiple arguments.

my.filter <- quo(cyl > 4 & disp > 100)

filter(mtcars, !!my.filter)

    mpg cyl  disp  hp drat    wt  qsec vs am gear carb
1  21.0   6 160.0 110 3.90 2.620 16.46  0  1    4    4
2  21.0   6 160.0 110 3.90 2.875 17.02  0  1    4    4
3  21.4   6 258.0 110 3.08 3.215 19.44  1  0    3    1
4  18.7   8 360.0 175 3.15 3.440 17.02  0  0    3    2
5  18.1   6 225.0 105 2.76 3.460 20.22  1  0    3    1
6  14.3   8 360.0 245 3.21 3.570 15.84  0  0    3    4
7  19.2   6 167.6 123 3.92 3.440 18.30  1  0    4    4
8  17.8   6 167.6 123 3.92 3.440 18.90  1  0    4    4
9  16.4   8 275.8 180 3.07 4.070 17.40  0  0    3    3

As Artem pointed out, you can, however, use the comma notation with the plural quos function and the !!! operator:

my.filter <- quos(cyl > 4, disp > 100)

filter(mtcars, !!!my.filter)