CODEWITHSUNDEEP
rfunction
Nneka
Nneka

Reputation: 1860

flexible number of arguments in R function

I have written a function to create plots, which looks something like this: 

getSecPlot <- function(data, xvar, yvar, yvarsec, groupvar, ...){

  sec_plot <- ggplot(data, aes_string (x = xvar, group = groupvar)) +
      geom_col(aes_string(y = yvar, fill = groupvar, alpha = 0.5), position = "dodge") +
      geom_line(aes(y = yvarsec,  color = gender)) 

  }

I would like to change this function. Sometimes there is no groupvar. In that case, i woule like to have a plot such as: 

  sec_plot <- ggplot(data, aes_string (x = xvar, group = 1)) +
      geom_col(aes_string(y = yvar), fill = "green") +
      geom_line(aes(y = yvarsec,  color = gender))

So, i would like to put this together in a single function. Something like: 

getSecPlot <- function(data, xvar, yvar, yvarsec, ...){

if (exists groupvar){

  sec_plot <- ggplot(data, aes_string (x = xvar, group = groupvar)) +
      geom_col(aes_string(y = yvar, fill = groupvar, alpha = 0.5), position = "dodge") +
      geom_line(aes(y = yvarsec,  color = gender)) 

} else {

      sec_plot <- ggplot(data, aes_string (x = xvar, group = 1)) +
          geom_col(aes_string(y = yvar), fill = "green") +
          geom_line(aes(y = yvarsec,  color = gender)) 

  }

the if (exists groupvar) is just for illustration - how could i check if the argument has been assigned in R ?

I am unsure about how the ... works. Once i took the groupvar out from the functions argument, the function did no longer work: 

getSecPlot <- function(data, xvar, yvar, yvarsec, ...){

  sec_plot <- ggplot(data, aes_string (x = xvar, group = groupvar)) +
      geom_col(aes_string(y = yvar, fill = groupvar, alpha = 0.5), position = "dodge") +
      geom_line(aes(y = yvarsec,  color = gender)) 

  }

plot.SeverityYearly <- getSecPlot(freqSevDataAge, xvar = "agegroup", yvar = "severity", yvarsec = "frequency", groupvar = "gender")

Error in aes_string(x = xvar, group = groupvar) : object 'groupvar' not found

Upvotes: 0

Views: 50

Answers (1)

Ronak Shah
Ronak Shah

Reputation: 388982

You can use missing to check if group_var is present. See this simple example : 

temp <- function(a, b, group_var) {
   if(missing(group_var))
      a + b
   else
      a + b + group_var
}

temp(1, 2, 3)
#[1] 6
temp(1, 2)
#[1] 3

Upvotes: 2

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