Given two ggplots, we can arange them side-by-side

```
library(ggplot2)
library(gridExtra)

# Data
data(iris)
df <- data.frame(y = rnorm(100))

# Plotting
p1 <- qplot(data=iris, Sepal.Width, Sepal.Length)
p2 <- ggplot(df, aes(x=1:100, y=y)) + geom_line()
grid.arrange(p1, p2, ncol=2)

```

[![plots 1](https://i.stack.imgur.com/Avlkz.png)](https://i.stack.imgur.com/Avlkz.png)

How can we do it if one of the plots is a `ggpair` object?

```
library(GGally)
p1 <- ggpairs(iris, colours='Species')
p2 <- ggplot(df, aes(x=1:100, y=y)) + geom_line()
grid.arrange(l, p2, ncol=6)
# Error in gList(list(list(data = list(Sepal.Length = c(5.1, 4.9, 4.7, 
#  4.6,  : only 'grobs' allowed in "gList"

```