R ggplot2 - geom_point custom color ranges and colors

Question

I'm trying to generalize a set of plots I regularly need through a function - I have trouble in getting some aspects right in there.

myCustomScatter <- function(df, col_x, col_y, col_z){
  p1 <- ggplot(df, aes(x=df[,col_x]))
  p1 <- p1 + geom_point(aes(y=df[,col_y], color=df[,col_z]))
  p1 <- p1 + scale_x_continuous(name=colnames(df)[col_x])
  p1 <- p1 + scale_y_continuous(name=colnames(df)[col_y])
  return(p1)
}

df1 <- data.frame(a=seq(1.1,9.9,1.1), b=seq(0.1,0.9,0.1), c=rev(seq(10.1, 99.9, 11.1)))

myCustomScatter(df1, 1, 2, 3)

This gives the following plot as expected.

1. I need the color ranges to be discrete based on df[,3] values- I need blue for value > 90, green for 90 >= value > 70, yellow for 70 >= value > 55, orange for 55 >= value > 25 & red for value <= 25 - how do I specify this ?

2. I need the title of the legend instead of df[,col_z] to be c which I can get through colnames(df1)[3] - how do I specify this ?

Answer 1

You can try this:

myCustomScatter <- function(df, col_x, col_y, col_z){
  p1 <- ggplot(df, aes_string(x=df[,col_x], color = cut(df[,col_z], c(-Inf, 25, 55, 70, 90, Inf))), size = 6)
  p1 <- p1 + geom_point(aes_string(y=df[,col_y]))
  p1 <- p1 + scale_x_continuous(name=colnames(df)[col_x])
  p1 <- p1 + scale_y_continuous(name=colnames(df)[col_y]) # + guides(color=guide_legend('c'))
  p1 <- p1 + scale_color_manual(name = names(df)[col_z],
                                values = c("red",
                                           "orange",
                                           "yellow",
                                           "green",
                                           "blue"))
  return(p1)
}

df1 <- data.frame(a=seq(1.1,9.9,1.1), b=seq(0.1,0.9,0.1), c=rev(seq(10.1, 99.9, 11.1)))

myCustomScatter(df1, 1, 2, 3)

Answer 2

use aes_string if you don't know the variable names in advance,

myCustomScatter <- function(df, col_x, col_y, col_z){

  ggplot(df, aes_string(x=names(df)[col_x], y = names(df)[col_y])) + 
    geom_point(aes_string(colour=names(df)[col_z])) + 
    scale_x_continuous(names(df)[col_x]) + 
    scale_y_continuous(names(df)[col_y]) +
    scale_color_gradientn(colours = terrain.colors(5))
}

df1 <- data.frame(a=seq(1.1,9.9,1.1), b=seq(0.1,0.9,0.1), c=rev(seq(10.1, 99.9, 11.1)))

myCustomScatter(df1, 1, 2, 3)