Accessing Private Methods from an R6 Class

August 13, 2017

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I recently wrote a package to solve the Twitter Waterflow Problem using an R6 class. You can view the package here and read about how I approached the problem here. In this blog post, I want to highlight how you can access private members of an R6 class which Winston Chang mentioned in his useR!2017 talk. I will use the waterflow package for this example. Within the R6 waterflow class there is a private member function, or method, that converts the data you provide the class with, and the data it calculates, into a tidy data.frame used for generating a plot. However what if we already have the data that this function needs to be supplied with? How can we just run this function on the fly? If we try to call it directly, we get an error.

wall <- c(2, 5, 1, 2, 3, 4, 7, 7, 6)
water <- c(2, 5, 1, 2, 3, 4, 7, 7, 6)
p <- waterflow$new(wall)
p$tidyWater(water, wall)
# Error in eval(expr, envir, enclos): attempt to apply non-function

Instead, what we need to do is extract the method from the class’ environment, .__enclos_env__, which allows us access to private members of the class.

p$.__enclos_env__$private$tidyWater(water, wall)
#    pos  type val
# 1    1 water   2
# 2    2 water   5
# 3    3 water   1
# 4    4 water   2
# 5    5 water   3
# 6    6 water   4
# 7    7 water   7
# 8    8 water   7
# 9    9 water   6
# 10   1  wall   2
# 11   2  wall   5
# 12   3  wall   1
# 13   4  wall   2
# 14   5  wall   3
# 15   6  wall   4
# 16   7  wall   7
# 17   8  wall   7
# 18   9  wall   6

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