CODEWITHSUNDEEP
rggplot2
Wooheon
Wooheon

Reputation: 339

Why use do.call here?

This is an example of ggplot2 Elegant Graphics for Data Analysis

geom_mean <- function(..., bar.params = list(), errorbar.params = list()) {
  params <- list(...)
  bar.params <- modifyList(params, bar.params)
  errorbar.params <- modifyList(params, errorbar.params)

  bar <- do.call("stat_summary", modifyList(
    list(fun.y = "mean", geom = "bar", fill = "grey70"),
    bar.params)
  )
  errorbar <- do.call("stat_summary", modifyList(
    list(fun.data = "mean_cl_normal", geom = "errorbar", width = 0.4),
    errorbar.params)
  )

  list(bar, errorbar)
}

It shows

enter image description here

In this code, what's do.call() roll?

I don't know why this code needs do.call().

What is the another function to replace do.call()?

Upvotes: 0

Views: 88

Answers (1)

Alexey
Alexey

Reputation: 190

do.call invokes a function using arguments provided as a list.
For example, 

 do.call("plot", list(x = 1:10, y = 1:10))

will result to 

plot(x = 1:10, y = 1:10)

Such approach allows to work with arbitrary argument number, which are caught by 

params <- list(...)

Then you can first modify some of them as you wish and later call the function stat_summary with this modified list:

do.call("stat_summary", params)

The reason is that stat_summary itself takes an arbitrary number of arguments (see ... in its documentation). If you are to describe all possible argument names, which user might provide, it would result to a lot of unflexible code (imagine, that stat_summary will get more options in the next version and have always to update your code accordingly).

Upvotes: 2

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