R color scatter plot points based on values

Question

I am able to plot a scatter plot and color the points based on one criteria, i.e. I can color all points >=3 as red and the remainder as black. I would love to be able to color points in this fashion:

1. =3 color red

2. <=1 color blue
3. The rest as black

The code I have below completes step 1 and 3 but I am not sure how to incorporate the second argument of step 2

data<- read.table('sample_data.txtt', header=TRUE, row.name=1)
pos<- data$col_name1
cn<- data$col_name2
plot(pos,cn, ylim=c(0,5), col="blue")
plot(pos,cn, col=ifelse(cn>=3,"red","black"), ylim=c(0,10))

Any help would be great!!! Thanks in advance

Answer 1

Best thing to do here is to add a column to the data object to represent the point colour. Then update sections of it by filtering.

data<- read.table('sample_data.txtt', header=TRUE, row.name=1)
# Create new column filled with default colour
data$Colour="black"
# Set new column values to appropriate colours
data$Colour[data$col_name2>=3]="red"
data$Colour[data$col_name2<=1]="blue"
# Plot all points at once, using newly generated colours
plot(data$col_name1,data$col_name2, ylim=c(0,5), col=data$Colour, ylim=c(0,10))

It should be clear how to adapt this for plots with more colours & conditions.