For statement don't work in ggplot function

Question

I've got a dataset with 3 columns but I need a generic function which can be apply to a dataset with more columns :

library(ggplot2)
library(plyr)
library(dplyr)

baseball[, c(2,6)]
D <- ddply(baseball[, c(2,6)], .(year), summarise, 
      g = sum(g, na.rm = T))
D$gCumulate <- round(cummean(D$g))

I want the same plot as :

g <- ggplot(D, aes(D[,1]))
g <- g + geom_line(aes(y=D[,2]), color="black")
g <- g + geom_line(aes(y=D[,3]), color="red")

And I don't understand why this works :

plotSimpleFuntion <- function(data=D, type, color) {
  names <- colnames(data)
  colnames(data) <- letters[1:length(data)]
  g <- ggplot(data, aes(data[,1]))
  if(type[1] == "line"){g <- g + geom_line(aes(y=data[,2]), color=color[1])}
  if(type[1] == "bar"){g <- g + geom_bar(aes(y=data[,2]), stat = 'identity',fill=color[1])}
  if(type[1] == "point"){g <- g + geom_point(aes(y=data[,2]), color=color[1])}
  if(type[1] == "area"){g <- g + geom_area(aes(y=data[,2]), fill=color[1])}
  if(type[2] == "line"){g <- g + geom_line(aes(y=data[,3]), color=color[2])}
  if(type[2] == "bar"){g <- g + geom_bar(aes(y=data[,3]), stat = 'identity',fill=color[2])}
  if(type[2] == "point"){g <- g + geom_point(aes(y=data[,3]), color=color[2])}
  if(type[2] == "area"){g <- g + geom_area(aes(y=data[,3]), fill=color[2])}
  g + xlab(names[1])
}

plotSimpleFuntion(D, type = c("line", 'line'), color = c("black","red"))

And not that :

plotSimpleFuntion <- function(data=D, type, color) {
  names <- colnames(data)
  colnames(data) <- letters[1:length(data)]
  g <- ggplot(data, aes(data[,1]))
  for (i in 1:2) {
    if(type[i] == "line"){g <- g + geom_line(aes(y=data[,i+1]), color=color[i])}
    if(type[i] == "bar"){g <- g + geom_bar(aes(y=data[,i+1]), stat = 'identity',fill=color[i])}
    if(type[i] == "point"){g <- g + geom_point(aes(y=data[,i+1]), color=color[i])}
    if(type[i] == "area"){g <- g + geom_area(aes(y=data[,i+1]), fill=color[i])}
  }
  g + xlab(names[1])
}

plotSimpleFuntion(D, type = c("line", 'line'), color = c("black","red"))

user_1412059 · Answer

I'm pretty sure the issue is that data[i + 1] etc. gets evaluated when the ggplot object is printed, i.e., after the loop. When this happens, i has the value 2.

Anyway, your approach is not using ggplot2 as intended. Here is an example how it should be used. Some more work would be needed to implement exactly what you are intending but I don't think you should do that anyway.

library(reshape2)
plotSimpleFuntion <- function(data=D, type, color) {
  n <- names(D)
  data <- melt(data, id.var = n[[1]])
  geom <- switch(type,
                 line = geom_line,
                 bar = geom_col,
                 point = geom_point,
                 area = geom_area)
  ggplot(data, aes_string(x = names(data)[[1]], y = "value", 
                          color = "variable", fill = "variable")) + 
    geom() +
    scale_color_manual(breaks = n[-1], values = color) +
    scale_fill_manual(breaks = n[-1], values = color)
}

plotSimpleFuntion(D, type = "line", color = c("black","red"))

This follows the grammar of graphics as intended but can't mix different geoms. You'll need an if condition to handle that by different code (e.g., without the melt). I'd advise against it.

For statement don't work in ggplot function

1 Answers