order_by: A helper function for ordering window function output.
In sctyner/dplyr050: A Grammar of Data Manipulation

Description Usage Arguments Details Examples

This is a useful function to control the order of window functions in R that don't have a specific ordering parameter. When translated to SQL it will modify the order clause of the OVER function.

1	order_by(order_by, call)

`order_by`	a vector to order_by
`call`	a function call to a window function, where the first argument is the vector being operated on

This function works by changing the call to instead call with_order with the appropriate arguments.

order_by(10:1, cumsum(1:10))
x <- 10:1
y <- 1:10
order_by(x, cumsum(y))

df <- data.frame(year = 2000:2005, value = (0:5) ^ 2)
scrambled <- df[sample(nrow(df)), ]

wrong <- mutate(scrambled, running = cumsum(value))
arrange(wrong, year)

right <- mutate(scrambled, running = order_by(year, cumsum(value)))
arrange(right, year)