%>% is called the forward pipe operator in R. It provides a mechanism for chaining commands with a new forward-pipe operator, %>%. This operator will forward a value, or the result of an expression, into the next function call/expression.
It is defined by the package magrittr (CRAN) and is heavily used by dplyr (CRAN).
The role of this function is to pass the left-hand side of the operator to the first argument of the right-hand side of the operator.
For example:
mtcars %>% head()
mpg cyl disp hp drat wt qsec vs am gear carb
Mazda RX4 21.0 6 160 110 3.90 2.620 16.46 0 1 4 4
Mazda RX4 Wag 21.0 6 160 110 3.90 2.875 17.02 0 1 4 4
Datsun 710 22.8 4 108 93 3.85 2.320 18.61 1 1 4 1
Hornet 4 Drive 21.4 6 258 110 3.08 3.215 19.44 1 0 3 1
Hornet Sportabout 18.7 8 360 175 3.15 3.440 17.02 0 0 3 2
Valiant 18.1 6 225 105 2.76 3.460 20.22 1 0 3 1
Thus, mtcars %>% head() is equivalent to head(mtcars).
Often, %>% is called multiple times to "chain" functions together, which accomplishes the same result as nesting. For example in the chain below, mtcarspassed to head(), then the result of that is passed to summary().
mtcars %>% head() %>% summary()
