What's the difference between facet_wrap() and facet_grid() in ggplot2?

Question

I've been reading the `ggplot2` documentation for both functions. I was wondering what were the differences and what would be right situation for using each function (`facet_wrap()` and `facet_grid()`). ``` library(ggplot2) p <- qplot(displ, hwy, data = mpg) p + facet_wrap(~ cyl) p + facet_grid(~ cyl) ``` I provide this small example to serve as starting point. The difference seems to be wrap makes the plots more autonomous and grid makes one plot all together.

Accepted Answer

The answer below refers to the case when you have 2 arguments in `facet_grid()` or `facet_wrap()`.

`facet_grid(x ~ y)` will display `x*y` plots even if some plots are empty. Ex:

```
library(ggplot2)
g <- ggplot(mpg, aes(displ, hwy))
```

There are 4 distinct cyl and 7 distinct class values.

```
g + geom_point(alpha=1/3) + facet_grid(cyl~class)
```

The above displays 4 * 7 = 28 plots, even if some are empty (because some classes do not have corresponding cylinder values, like rows with class="midsize" doesn't have any corresponding cyl="5" value ) `facet_wrap(x ~ y)` on the other hand, displays only the plots having actual values.

```
g + geom_point(alpha=1/3) + facet_wrap(cyl~class)
```

There are 19 plots displayed now, one for every combination of cyl and class.

What's the difference between facet_wrap() and facet_grid() in ggplot2?

Solution

Problem