CODEWITHSUNDEEP
rggplot2
Nilly
Nilly

Reputation: 103

R - How to initialize *or* add to ggplot, using only one function

I have a function in R that reads data off a website and plots 2 columns. How can I make it so that the first time I run the function it initializes a new graph, but then subsequent runs (which will be marked with a 'reset' parameter) will add a new set of points to the graph rather than overwriting the old one?

getdata<- function(team,year,reset=F){

#Retrieve/format Data
[..]

#Plot Data
if (reset==T)
{
    p <-ggplot(data, aes(x = no, y = pts)) +
        geom_path(colour="red", size=2) +
        geom_point(colour="black" ,size = 2, shape=21, fill="white") 
        return(p)
}
else
{
     add<-ggplot(data, aes(x = no, y = pts)) +
      geom_path(colour = "blue", size = 2) +
      geom_point(colour="black", size = 2, shape=21,  fill="white")             

              p <- p + add
      return(p)
}

I think my issue is similar to this posted here: Adding line with points to a plot in ggplot2 but I'm having some trouble adding the it as a list to the currently existing plot.

I'm a beginner with R so might be doing something stupid!

Thanks for any help, been wrestling with this for a while.

Upvotes: 1

Views: 927

Answers (1)

BrodieG
BrodieG

Reputation: 52687

There are a few things that need to happen for this to work:

  1. Your function needs as mechanism to store the previous plot
  2. You want to add layers (e.g. geom_point()) to your plot, not an entire ggplot object

So here is a potential implementation (note, untested since your example is not reproducible):

make_getdata <- function() {                      # THIS FUNCTION RETURNS A FUNCTION
  p <- NULL                                       # WE WILL STORE PLOT HERE
  function(team,year,reset=F) {
    # get data
    if(reset || is.null(p)) {
      p <<- ggplot(data, aes(x = no, y = pts)) +  # NOTICE DOUBLE ARROW
        geom_path(colour="red", size=2) +
        geom_point(colour="black" ,size = 2, shape=21, fill="white") 
    } else {
      p <<- p +                                   # NOTICE DOUBLE ARROW
        geom_path(data=data, aes(x = no, y = pts), colour = "blue", size = 2) +
        geom_point(data=data, aes(x = no, y = pts), colour="black", size = 2, shape=21,  fill="white")
    }
    return(p)
} }
getdata <- make_getdata()   # this creates your `getdata` function and stores it in `getdata`
getdata(...)

The key here is we take advantage of R's scoping properties to create a persistent variable were we store the graph. make_getdata() creates a function as well as a function environment. That environment contains p, which we can use to store our plots with <<-.

Upvotes: 2

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